Initial implementation.

LICENSE

@@ -0,0 +1,13 @@
+Copyright (c) 2012-2013 Dave Collins <dave@davec.name>
+
+Permission to use, copy, modify, and distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

spew/common.go

@@ -0,0 +1,241 @@
+/*
+ * Copyright (c) 2013 Dave Collins <dave@davec.name>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+package spew
+
+import (
+	"fmt"
+	"io"
+	"reflect"
+	"strconv"
+	"unsafe"
+)
+
+// reflectValue mirrors the struct layout of the reflect package Value type.
+var reflectValue struct {
+	typ  unsafe.Pointer
+	val  unsafe.Pointer
+	flag uintptr
+}
+
+// flagIndir indicates whether the value field of a reflect.Value is the actual
+// data or a pointer to the data.
+const flagIndir = 1 << 1
+
+// unsafeReflectValue converts the passed reflect.Value into a one that bypasses
+// the typical safety restrictions preventing access to unaddressable and
+// unexported data.  It works by digging the raw pointer to the underlying
+// value out of the protected value and generating a new unprotected (unsafe)
+// reflect.Value to it.
+//
+// This allows us to check for implementations of the Stringer and error
+// interfaces to be used for pretty printing ordinarily unaddressable and
+// inaccessible values such as unexported struct fields.
+func unsafeReflectValue(v reflect.Value) (rv reflect.Value) {
+	indirects := 1
+	vt := v.Type()
+	upv := unsafe.Pointer(uintptr(unsafe.Pointer(&v)) + unsafe.Offsetof(reflectValue.val))
+	rvf := *(*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(&v)) + unsafe.Offsetof(reflectValue.flag)))
+	if rvf&flagIndir != 0 {
+		vt = reflect.PtrTo(v.Type())
+		indirects++
+	}
+
+	pv := reflect.NewAt(vt, upv)
+	rv = pv
+	for i := 0; i < indirects; i++ {
+		rv = rv.Elem()
+	}
+	return rv
+}
+
+// Some constants in the form of bytes to avoid string overhead.  This mirrors
+// the technique used in the fmt package.
+var (
+	panicBytes            = []byte("(PANIC=")
+	plusBytes             = []byte("+")
+	iBytes                = []byte("i")
+	trueBytes             = []byte("true")
+	falseBytes            = []byte("false")
+	interfaceBytes        = []byte("(interface {}) ")
+	commaNewlineBytes     = []byte(",\n")
+	newlineBytes          = []byte("\n")
+	openBraceBytes        = []byte("{")
+	openBraceNewlineBytes = []byte("{\n")
+	closeBraceBytes       = []byte("}")
+	closeBraceNewlinBytes = []byte("}\n")
+	asteriskBytes         = []byte("*")
+	colonSpaceBytes       = []byte(": ")
+	openParenBytes        = []byte("(")
+	closeParenBytes       = []byte(")")
+	spaceBytes            = []byte(" ")
+	pointerChainBytes     = []byte("->")
+	nilAngleBytes         = []byte("<nil>")
+	maxNewlineBytes       = []byte("<max depth reached>\n")
+	maxShortBytes         = []byte("<max>")
+	circularBytes         = []byte("<already shown>")
+	circularShortBytes    = []byte("<shown>")
+	invalidAngleBytes     = []byte("<invalid>")
+	percentBytes          = []byte("%")
+	precisionBytes        = []byte(".")
+	openAngleBytes        = []byte("<")
+	closeAngleBytes       = []byte(">")
+	openMapBytes          = []byte("map[")
+	closeMapBytes         = []byte("]")
+)
+
+// hexDigits is used to map a decimal value to a hex digit.
+var hexDigits = "0123456789abcdef"
+
+// unpackValue returns values inside of non-nil inteferfaces when possible.
+// This is useful for data types like structs, arrays, slices, and maps which
+// can contain varying types packed inside an interface.
+func unpackValue(v reflect.Value) reflect.Value {
+	if v.Kind() == reflect.Interface && !v.IsNil() {
+		v = v.Elem()
+	}
+	return v
+}
+
+// catchPanic handles any panics that might occur during the handleMethods
+// calls.
+func catchPanic(w io.Writer, v reflect.Value) {
+	if err := recover(); err != nil {
+		w.Write(panicBytes)
+		fmt.Fprintf(w, "%v", err)
+		w.Write(closeParenBytes)
+	}
+}
+
+// handleMethods attempts to call the Error and String methods on the underlying
+// type the passed reflect.Value represents and outputes the result to Writer w.
+//
+// It handles panics in any called methods by catching and displaying the error
+// as the formatted value.
+func handleMethods(w io.Writer, v reflect.Value) (handled bool) {
+	// We need an interface to check if the type implements the error or
+	// Stringer interface.  However, the reflect package won't give us an
+	// an interface on certain things like unexported struct fields in order
+	// to enforce visibility rules.  We use unsafe to bypass these restrictions
+	// since this package does not mutate the values.
+	if !v.CanInterface() {
+		v = unsafeReflectValue(v)
+	}
+
+	// Choose whether or not to do error and Stringer interface lookups against
+	// the base type or a pointer to the base type depending on settings.
+	// Technically calling one of these methods with a pointer receiver can
+	// mutate the value, however, types which choose to satisify an error or
+	// Stringer interface with a pointer receiver should not be mutating their
+	// state inside these interface methods.
+	var viface interface{}
+	if !Config.DisablePointerMethods {
+		if !v.CanAddr() {
+			v = unsafeReflectValue(v)
+		}
+		viface = v.Addr().Interface()
+	} else {
+		viface = v.Interface()
+	}
+
+	// Is it an error or Stringer?
+	switch iface := viface.(type) {
+	case error:
+		defer catchPanic(w, v)
+		w.Write([]byte(iface.Error()))
+		return true
+
+	case fmt.Stringer:
+		defer catchPanic(w, v)
+		w.Write([]byte(iface.String()))
+		return true
+	}
+	return false
+}
+
+// printBool outputs a boolean value as true or false to Writer w.
+func printBool(w io.Writer, val bool) {
+	if val {
+		w.Write(trueBytes)
+	} else {
+		w.Write(falseBytes)
+	}
+}
+
+// printInt outputs a signed integer value to Writer w.
+func printInt(w io.Writer, val int64) {
+	w.Write([]byte(strconv.FormatInt(val, 10)))
+}
+
+// printUint outputs an unsigned integer value to Writer w.
+func printUint(w io.Writer, val uint64) {
+	w.Write([]byte(strconv.FormatUint(val, 10)))
+}
+
+// printFloat outputs a floating point value using the specified precision,
+// which is expected to be 32 or 64bit, to Writer w.
+func printFloat(w io.Writer, val float64, precision int) {
+	w.Write([]byte(strconv.FormatFloat(val, 'g', -1, precision)))
+}
+
+// printComplex outputs a complex value using the specified float precision
+// for the real and imaginary parts to Writer w.
+func printComplex(w io.Writer, c complex128, floatPrecision int) {
+	r := real(c)
+	w.Write(openParenBytes)
+	w.Write([]byte(strconv.FormatFloat(r, 'g', -1, floatPrecision)))
+	i := imag(c)
+	if i >= 0 {
+		w.Write(plusBytes)
+	}
+	w.Write([]byte(strconv.FormatFloat(i, 'g', -1, floatPrecision)))
+	w.Write(iBytes)
+	w.Write(closeParenBytes)
+}
+
+// printHexPtr outputs a uintptr formatted as hexidecimal with a leading '0x'
+// prefix to Writer w.
+func printHexPtr(w io.Writer, p uintptr) {
+	// Null pointer.
+	num := uint64(p)
+	if num == 0 {
+		w.Write(nilAngleBytes)
+		return
+	}
+
+	// Max uint64 is 16 bytes in hex + 2 bytes for '0x' prefix
+	buf := make([]byte, 18)
+
+	// It's simpler to construct the hex string right to left.
+	base := uint64(16)
+	i := len(buf) - 1
+	for num >= base {
+		buf[i] = hexDigits[num%base]
+		num /= base
+		i--
+	}
+	buf[i] = hexDigits[num]
+
+	// Add '0x' prefix.
+	i--
+	buf[i] = 'x'
+	i--
+	buf[i] = '0'
+
+	// Strip unused leading bytes.
+	buf = buf[i:]
+	w.Write(buf)
+}

spew/config.go

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2013 Dave Collins <dave@davec.name>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+package spew
+
+// ConfigState is used to describe configuration options used by spew to format
+// and display values.  There is currently only a single global instance, Config,
+// that is used to control all Formatter and Dump functionality.  This state
+// is designed so that it would be fairly simple to add the ability to have
+// unique config per Formatter or dumpState instance if there is demand for
+// such a feature.
+type ConfigState struct {
+	// MaxDepth controls the maximum number of levels to descend into nested
+	// data structures.  The default, 0, means there is no limit.
+	//
+	// NOTE: Circular data structures are properly detected, so it is not
+	// necessary to set this value unless you specifically want to limit deeply
+	// nested data structures.
+	MaxDepth int
+
+	// Indent specifies the string to use for each indentation level.  It is
+	// a single space by default.  If you would like more indentation, you might
+	// set this to a tab with "\t" or perhaps two spaces with "  ".
+	Indent string
+
+	// DisableMethods specifies whether or not error and Stringer interfaces are
+	// invoked for types that implement them.
+	DisableMethods bool
+
+	// DisablePointerMethods specifies whether or not to check for and invoke
+	// error and Stringer interfaces on types which only accept a pointer
+	// receiver when the current type is not a pointer.
+	//
+	// NOTE: This might be an unsafe action since calling one of these methods
+	// with a pointer receiver could technically mutate the value, however,
+	// in practice, types which choose to satisify an error or Stringer
+	// interface with a pointer receiver should not be mutating their state
+	// inside these interface methods.
+	DisablePointerMethods bool
+}
+
+// Config is the active configuration in use by spew.  The configuration
+// can be changed by modifying the contents of spew.Config.
+var Config ConfigState = ConfigState{Indent: " "}

spew/doc.go

@@ -0,0 +1,148 @@
+/*
+ * Copyright (c) 2013 Dave Collins <dave@davec.name>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*
+Package spew implements a deep pretty printer for Go data structures to aid in
+debugging.
+
+A quick overview of the additional features spew provides over the built-in
+printing facilities for Go data types are as follows:
+
+	* Pointers are dereferenced and followed
+	* Circular data structures are detected and handled properly
+	* Custom error/Stringer interfaces are optionally invoked, including
+	  on unexported types
+	* Custom types which only implement the error/Stringer interfaces via
+	  a pointer receiver are optionally invoked when passing non-pointer
+	  variables
+
+There are two different approaches spew allows for dumping Go data structures:
+
+	* Dump style which prints with newlines, customizable indentation,
+	  and additional debug information such as types and all pointer addresses
+	  used to indirect to the final value
+	* A custom Formatter interface that integrates cleanly with the standard fmt
+	  package and replaces %v and %+v to provide inline printing similar
+	  to the default %v while providing the additional functionality outlined
+	  above and passing unsupported format verb/flag combinations such a %x,
+	  %q, and %#v along to fmt
+
+Quick Start
+
+This section demonstrates how to quickly get started with spew.  See the
+sections below for further details on formatting and configuration options.
+
+To dump a variable with full newlines, indentation, type, and pointer
+information use Dump or Fdump:
+	spew.Dump(myVar1, myVar2, ...)
+	spew.Fdump(someWriter, myVar1, myVar2, ...)
+
+Alternatively, if you would prefer to use format strings with a compacted inline
+printing style, use the convenience wrappers Printf, Fprintf, etc with either
+%v (most compact) or %+v (adds pointer addresses):
+	spew.Printf("myVar1: %v -- myVar2: %+v", myVar1, myVar2)
+	spew.Fprintf(someWriter, "myVar1: %v -- myVar2: %+v", myVar1, myVar2)
+
+Configuration Options
+
+The following configuration options are available:
+	spew.Config.MaxDepth
+		Maximum number of levels to descend into nested data structures.
+		There is no limit by default.
+
+	spew.Config.Indent
+		String to use for each indentation level for Dump functions.
+		It is a single space by default.  A popular alternative is "\t".
+
+	spew.Config.DisableMethods
+		Disables invocation of error and Stringer interface methods.
+		Method invocation is enabled by default.
+
+	spew.Config.DisablePointerMethods
+		Disables invocation of error and Stringer interface methods on types
+		which only accept pointer receivers from non-pointer variables.
+		Pointer method invocation is enabled by default.
+
+Dump Usage
+
+Simply call spew.Dump with a list of variables you want to dump:
+
+	spew.Dump(myVar1, myVar2, ...)
+
+You may also call spew.Fdump if you would prefer to output to an arbitrary
+io.Writer.  For example, to dump to standard error:
+
+	spew.Fdump(os.Stderr, myVar1, myVar2, ...)
+
+Sample Dump Output
+
+See the Dump example for details on the setup of the types and variables being
+shown here.
+
+	(main.Foo) {
+	 unexportedField: (*main.Bar)(0xf84002e210)({
+	  flag: (main.Flag) flagTwo,
+	  data: (uintptr) <nil>
+	 }),
+	 ExportedField: (map[interface {}]interface {}) {
+	  (string) "one": (bool) true
+	 }
+	}
+
+Custom Formatter
+
+Spew provides a custom formatter the implements the fmt.Formatter interface
+so that integrates cleanly with standard fmt package printing functions. The
+formatter is useful for inline printing of smaller data types similar to the
+standard %v format specifier.
+
+The spew formatter only responds to the %v and %+v verb combinations.  Any other
+variations such as %x, %q, and %#v will be sent to the the standard fmt package
+for formatting.  In addition, the spew formatter ignores the width and precision
+arguments (however they will still work on the format specifiers spew does not
+handle).
+
+Custom Formatter Usage
+
+The simplest way to make use of the spew custom formatter is to call one of the
+convenience functions such as spew.Printf, spew.Println, or spew.Printf.  The
+functions have the exact same syntax you are most likely already familiar with:
+
+	spew.Printf("myVar1: %v -- myVar2: %+v", myVar1, myVar2)
+	spew.Println(myVar, myVar2)
+	spew.Fprintf(os.Stderr, "myVar1: %v -- myVar2: %+v", myVar1, myVar2)
+
+See the Index for the full list convenience functions.
+
+Sample Formatter Output
+
+Double pointer to a uint8 via %v:
+	<**>5
+
+Circular struct with a uint8 field and a pointer to itself via %+v:
+	{ui8:1 c:<*>(0xf84002d200){ui8:1 c:<*>(0xf84002d200)<shown>}}
+
+See the Printf example for details on the setup of variables being shown
+here.
+
+Errors
+
+Since it is possible for custom error/Stringer interfaces to panic, spew
+detects them and handles them internally by printing the panic information
+inline with the output.  Since spew is intended to provide deep pretty printing
+capabilities on structures, it intentionally does not return any errors.
+*/
+package spew

spew/dump.go

@@ -0,0 +1,323 @@
+/*
+ * Copyright (c) 2013 Dave Collins <dave@davec.name>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+package spew
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"strconv"
+)
+
+// dumpState contains information about the state of a dump operation.
+type dumpState struct {
+	w              io.Writer
+	depth          int
+	pointers       map[uintptr]int
+	ignoreNextType bool
+	ignoreNextPad  bool
+}
+
+// pad performs indentation according to the depth level and Config.Indent
+// option.
+func (d *dumpState) pad() {
+	if d.ignoreNextPad {
+		d.ignoreNextPad = false
+		return
+	}
+	d.w.Write(bytes.Repeat([]byte(Config.Indent), d.depth))
+}
+
+// dumpPtr handles formatting of pointers by indirecting them as necessary.
+func (d *dumpState) dumpPtr(v reflect.Value) {
+	// Remove pointers at or below the current depth from map used to detect
+	// circular refs.
+	for k, depth := range d.pointers {
+		if depth >= d.depth {
+			delete(d.pointers, k)
+		}
+	}
+
+	// Keep list of all dereferenced pointers to show later.
+	pointerChain := make([]uintptr, 0)
+
+	// Figure out how many levels of indirection there are by derferencing
+	// pointers and unpacking interfaces down the chain while detecting circular
+	// references.
+	nilFound := false
+	cycleFound := false
+	indirects := 0
+	ve := v
+	for ve.Kind() == reflect.Ptr {
+		indirects++
+		if ve.IsNil() {
+			nilFound = true
+			break
+		}
+		addr := ve.Pointer()
+		pointerChain = append(pointerChain, addr)
+		if pd, ok := d.pointers[addr]; ok && pd < d.depth {
+			cycleFound = true
+			indirects--
+			break
+		}
+		d.pointers[addr] = d.depth
+
+		ve = ve.Elem()
+		if ve.Kind() == reflect.Interface {
+			if ve.IsNil() {
+				nilFound = true
+				break
+			}
+			ve = ve.Elem()
+		}
+	}
+
+	// Display type information.
+	d.w.Write(openParenBytes)
+	d.w.Write(bytes.Repeat(asteriskBytes, indirects))
+	d.w.Write([]byte(ve.Type().String()))
+	d.w.Write(closeParenBytes)
+
+	// Display pointer information.
+	d.w.Write(openParenBytes)
+	for i, addr := range pointerChain {
+		if i > 0 {
+			d.w.Write(pointerChainBytes)
+		}
+		printHexPtr(d.w, addr)
+	}
+	d.w.Write(closeParenBytes)
+
+	// Display dereferenced value.
+	d.w.Write(openParenBytes)
+	switch {
+	case nilFound == true:
+		d.w.Write(nilAngleBytes)
+
+	case cycleFound == true:
+		d.w.Write(circularBytes)
+
+	default:
+		d.ignoreNextType = true
+		d.dump(ve)
+	}
+	d.w.Write(closeParenBytes)
+}
+
+// dump is the main workhorse for dumping a value.  It uses the passed reflect
+// value to figure out what kind of object we are dealing with and formats it
+// appropriately.  It is a recursive function, however circular data structures
+// are detected and handled properly.
+func (d *dumpState) dump(v reflect.Value) {
+	// Handle pointers specially.
+	kind := v.Kind()
+	if kind == reflect.Ptr {
+		d.pad()
+		d.dumpPtr(v)
+		return
+	}
+
+	// Print type information unless already handled elsewhere.
+	if !d.ignoreNextType {
+		d.pad()
+		d.w.Write(openParenBytes)
+		d.w.Write([]byte(v.Type().String()))
+		d.w.Write(closeParenBytes)
+		d.w.Write(spaceBytes)
+	}
+	d.ignoreNextType = false
+
+	// Call error/Stringer interfaces if they exist and the handle methods flag
+	// is enabled
+	if !Config.DisableMethods {
+		if (kind != reflect.Invalid) && (kind != reflect.Interface) {
+			if handled := handleMethods(d.w, v); handled {
+				return
+			}
+		}
+	}
+
+	switch kind {
+	case reflect.Invalid:
+		d.w.Write(invalidAngleBytes)
+
+	case reflect.Bool:
+		printBool(d.w, v.Bool())
+
+	case reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Int:
+		printInt(d.w, v.Int())
+
+	case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uint:
+		printUint(d.w, v.Uint())
+
+	case reflect.Float32:
+		printFloat(d.w, v.Float(), 32)
+
+	case reflect.Float64:
+		printFloat(d.w, v.Float(), 64)
+
+	case reflect.Complex64:
+		printComplex(d.w, v.Complex(), 32)
+
+	case reflect.Complex128:
+		printComplex(d.w, v.Complex(), 64)
+
+	case reflect.Array, reflect.Slice:
+		d.w.Write(openBraceNewlineBytes)
+		d.depth++
+		if (Config.MaxDepth != 0) && (d.depth > Config.MaxDepth) {
+			d.pad()
+			d.w.Write(maxNewlineBytes)
+		} else {
+			numEntries := v.Len()
+			for i := 0; i < numEntries; i++ {
+				d.dump(unpackValue(v.Index(i)))
+				if i < (numEntries - 1) {
+					d.w.Write(commaNewlineBytes)
+				} else {
+					d.w.Write(newlineBytes)
+				}
+			}
+		}
+		d.depth--
+		d.pad()
+		d.w.Write(closeBraceBytes)
+
+	case reflect.String:
+		d.w.Write([]byte(strconv.Quote(v.String())))
+
+	case reflect.Interface:
+		// Do nothing.  We should never get here due to unpackValue calls.
+
+	case reflect.Ptr:
+		// Do nothing.  We should never get here since pointer have already
+		// been handled above.
+
+	case reflect.Map:
+		d.w.Write(openBraceNewlineBytes)
+		d.depth++
+		if (Config.MaxDepth != 0) && (d.depth > Config.MaxDepth) {
+			d.pad()
+			d.w.Write(maxNewlineBytes)
+		} else {
+			numEntries := v.Len()
+			keys := v.MapKeys()
+			for i, key := range keys {
+				d.dump(unpackValue(key))
+				d.w.Write(colonSpaceBytes)
+				d.ignoreNextPad = true
+				d.dump(unpackValue(v.MapIndex(key)))
+				if i < (numEntries - 1) {
+					d.w.Write(commaNewlineBytes)
+				} else {
+					d.w.Write(newlineBytes)
+				}
+			}
+		}
+		d.depth--
+		d.pad()
+		d.w.Write(closeBraceBytes)
+
+	case reflect.Struct:
+		d.w.Write(openBraceNewlineBytes)
+		d.depth++
+		if (Config.MaxDepth != 0) && (d.depth > Config.MaxDepth) {
+			d.pad()
+			d.w.Write(maxNewlineBytes)
+		} else {
+			vt := v.Type()
+			numFields := v.NumField()
+			for i := 0; i < numFields; i++ {
+				d.pad()
+				vtf := vt.Field(i)
+				d.w.Write([]byte(vtf.Name))
+				d.w.Write(colonSpaceBytes)
+				d.ignoreNextPad = true
+				d.dump(unpackValue(v.Field(i)))
+				if i < (numFields - 1) {
+					d.w.Write(commaNewlineBytes)
+				} else {
+					d.w.Write(newlineBytes)
+				}
+			}
+		}
+		d.depth--
+		d.pad()
+		d.w.Write(closeBraceBytes)
+
+	case reflect.Uintptr:
+		printHexPtr(d.w, uintptr(v.Uint()))
+
+	case reflect.UnsafePointer, reflect.Chan, reflect.Func:
+		printHexPtr(d.w, v.Pointer())
+
+	// There were not any other types at the time this code was written, but
+	// fall back to letting the default fmt package handle it in case any new
+	// types are added.
+	default:
+		if v.CanInterface() {
+			fmt.Fprintf(d.w, "%v", v.Interface())
+		} else {
+			fmt.Fprintf(d.w, "%v", v.String())
+		}
+	}
+}
+
+// Fdump formats and displays the passed arguments to io.Writer w.  It formats
+// exactly the same as Dump.
+func Fdump(w io.Writer, a ...interface{}) {
+	for _, arg := range a {
+		if arg == nil {
+			w.Write(interfaceBytes)
+			w.Write(nilAngleBytes)
+			w.Write(newlineBytes)
+			continue
+		}
+
+		d := dumpState{w: w}
+		d.pointers = make(map[uintptr]int)
+		d.dump(reflect.ValueOf(arg))
+		d.w.Write(newlineBytes)
+	}
+}
+
+/*
+Dump displays the passed parameters to standard out with newlines, customizable
+indentation, and additional debug information such as complete types and all
+pointer addresses used to indirect to the final value.  It provides the
+following features over the built-in printing facilities provided by the fmt
+package:
+
+	* Pointers are dereferenced and followed
+	* Circular data structures are detected and handled properly
+	* Custom error/Stringer interfaces are optionally invoked, including
+	  on unexported types
+	* Custom types which only implement the error/Stringer interfaces via
+	  a pointer receiver are optionally invoked when passing non-pointer
+	  variables
+
+The configuration options are controlled by an exported package global,
+spew.Config.  See ConfigState for options documentation.
+
+See Fdump if you would prefer dump to an arbitrary io.Writer.
+*/
+func Dump(a ...interface{}) {
+	Fdump(os.Stdout, a...)
+}

spew/dump_test.go

@@ -0,0 +1,675 @@
+/*
+ * Copyright (c) 2013 Dave Collins <dave@davec.name>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*
+Test Summary:
+NOTE: For each test, a pointer and double pointer to the base test element
+are also tested to ensure proper indirection across all types.
+
+- Max int8, int16, int32, int64, int
+- Max uint8, uint16, uint32, uint64, uint
+- Boolean true and false
+- Standard complex64 and complex128
+- Array containing standard ints
+- Array containing type with custom formatter on pointer receiver only
+- Slice containing standard float32 values
+- Slice containing type with custom formatter on pointer receiver only
+- Standard string
+- Nil interface
+- Map with string keys and int vals
+- Map with custom formatter type on pointer receiver only keys and vals
+- Map with interface keys and values
+- Struct with primitives
+- Struct that contains another struct
+- Struct that contains custom type with Stringer pointer interface via both
+  exported and unexported fields
+- Uintptr to 0 (null pointer)
+- Uintptr address of real variable
+- Unsafe.Pointer to 0 (null pointer)
+- Unsafe.Pointer to address of real variable
+- Nil channel
+- Standard int channel
+- Function with no params and no returns
+- Function with param and no returns
+- Function with multiple params and multiple returns
+- Struct that is circular through self referencing
+- Structs that are circular through cross referencing
+- Structs that are indirectly circular
+*/
+
+package spew_test
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/davecgh/go-spew/spew"
+	"testing"
+	"unsafe"
+)
+
+// custom type to test Stinger interface on pointer receiver.
+type pstringer string
+
+// String implements the Stringer interface for testing invocation of custom
+// stringers on types with only pointer receivers.
+func (s *pstringer) String() string {
+	return "stringer " + string(*s)
+}
+
+// xref1 and xref2 are cross referencing structs for testing circular reference
+//  detection.
+type xref1 struct {
+	ps2 *xref2
+}
+type xref2 struct {
+	ps1 *xref1
+}
+
+// indirCir1, indirCir2, and indirCir3 are used to generate an indirect circular
+// reference for testing detection.
+type indirCir1 struct {
+	ps2 *indirCir2
+}
+type indirCir2 struct {
+	ps3 *indirCir3
+}
+type indirCir3 struct {
+	ps1 *indirCir1
+}
+
+// dumpTest is used to describe a test to be perfomed against the Dump method.
+type dumpTest struct {
+	in   interface{}
+	want string
+}
+
+// dumpTests houses all of the tests to be performed against the Dump method.
+var dumpTests = make([]dumpTest, 0)
+
+// addDumpTest is a helper method to append the passed input and desired result
+// to dumpTests
+func addDumpTest(in interface{}, want string) {
+	test := dumpTest{in, want}
+	dumpTests = append(dumpTests, test)
+}
+
+func addIntTests() {
+	// Max int8.
+	v := int8(127)
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "int8"
+	vs := "127"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Max int16.
+	v2 := int16(32767)
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "int16"
+	v2s := "32767"
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+
+	// Max int32.
+	v3 := int32(2147483647)
+	pv3 := &v3
+	v3Addr := fmt.Sprintf("%p", pv3)
+	pv3Addr := fmt.Sprintf("%p", &pv3)
+	v3t := "int32"
+	v3s := "2147483647"
+	addDumpTest(v3, "("+v3t+") "+v3s+"\n")
+	addDumpTest(pv3, "(*"+v3t+")("+v3Addr+")("+v3s+")\n")
+	addDumpTest(&pv3, "(**"+v3t+")("+pv3Addr+"->"+v3Addr+")("+v3s+")\n")
+
+	// Max int64.
+	v4 := int64(9223372036854775807)
+	pv4 := &v4
+	v4Addr := fmt.Sprintf("%p", pv4)
+	pv4Addr := fmt.Sprintf("%p", &pv4)
+	v4t := "int64"
+	v4s := "9223372036854775807"
+	addDumpTest(v4, "("+v4t+") "+v4s+"\n")
+	addDumpTest(pv4, "(*"+v4t+")("+v4Addr+")("+v4s+")\n")
+	addDumpTest(&pv4, "(**"+v4t+")("+pv4Addr+"->"+v4Addr+")("+v4s+")\n")
+
+	// Max int.
+	v5 := int(2147483647)
+	pv5 := &v5
+	v5Addr := fmt.Sprintf("%p", pv5)
+	pv5Addr := fmt.Sprintf("%p", &pv5)
+	v5t := "int"
+	v5s := "2147483647"
+	addDumpTest(v5, "("+v5t+") "+v5s+"\n")
+	addDumpTest(pv5, "(*"+v5t+")("+v5Addr+")("+v5s+")\n")
+	addDumpTest(&pv5, "(**"+v5t+")("+pv5Addr+"->"+v5Addr+")("+v5s+")\n")
+}
+
+func addUintTests() {
+	// Max uint8.
+	v := uint8(255)
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "uint8"
+	vs := "255"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Max uint16.
+	v2 := uint16(65535)
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "uint16"
+	v2s := "65535"
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+
+	// Max uint32.
+	v3 := uint32(4294967295)
+	pv3 := &v3
+	v3Addr := fmt.Sprintf("%p", pv3)
+	pv3Addr := fmt.Sprintf("%p", &pv3)
+	v3t := "uint32"
+	v3s := "4294967295"
+	addDumpTest(v3, "("+v3t+") "+v3s+"\n")
+	addDumpTest(pv3, "(*"+v3t+")("+v3Addr+")("+v3s+")\n")
+	addDumpTest(&pv3, "(**"+v3t+")("+pv3Addr+"->"+v3Addr+")("+v3s+")\n")
+
+	// Max uint64.
+	v4 := uint64(18446744073709551615)
+	pv4 := &v4
+	v4Addr := fmt.Sprintf("%p", pv4)
+	pv4Addr := fmt.Sprintf("%p", &pv4)
+	v4t := "uint64"
+	v4s := "18446744073709551615"
+	addDumpTest(v4, "("+v4t+") "+v4s+"\n")
+	addDumpTest(pv4, "(*"+v4t+")("+v4Addr+")("+v4s+")\n")
+	addDumpTest(&pv4, "(**"+v4t+")("+pv4Addr+"->"+v4Addr+")("+v4s+")\n")
+
+	// Max uint.
+	v5 := uint(4294967295)
+	pv5 := &v5
+	v5Addr := fmt.Sprintf("%p", pv5)
+	pv5Addr := fmt.Sprintf("%p", &pv5)
+	v5t := "uint"
+	v5s := "4294967295"
+	addDumpTest(v5, "("+v5t+") "+v5s+"\n")
+	addDumpTest(pv5, "(*"+v5t+")("+v5Addr+")("+v5s+")\n")
+	addDumpTest(&pv5, "(**"+v5t+")("+pv5Addr+"->"+v5Addr+")("+v5s+")\n")
+}
+
+func addBoolTests() {
+	// Boolean true.
+	v := bool(true)
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "bool"
+	vs := "true"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Boolean false.
+	v2 := bool(false)
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "bool"
+	v2s := "false"
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+}
+
+func addFloatTests() {
+	// Standard float32.
+	v := float32(3.1415)
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "float32"
+	vs := "3.1415"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Standard float64.
+	v2 := float64(3.1415926)
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "float64"
+	v2s := "3.1415926"
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+}
+
+func addComplexTests() {
+	// Standard complex64.
+	v := complex(float32(6), -2)
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "complex64"
+	vs := "(6-2i)"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Standard complex128.
+	v2 := complex(float64(-6), 2)
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "complex128"
+	v2s := "(-6+2i)"
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+}
+
+func addArrayTests() {
+	// Array containing standard ints.
+	v := [3]int{1, 2, 3}
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "int"
+	vs := "{\n (" + vt + ") 1,\n (" + vt + ") 2,\n (" + vt + ") 3\n}"
+	addDumpTest(v, "([3]"+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*[3]"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**[3]"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Array containing type with custom formatter on pointer receiver only.
+	v2 := [3]pstringer{"1", "2", "3"}
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "spew_test.pstringer"
+	v2s := "{\n (" + v2t + ") stringer 1,\n (" + v2t + ") stringer 2,\n (" +
+		v2t + ") stringer 3\n}"
+	addDumpTest(v2, "([3]"+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*[3]"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**[3]"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+}
+
+func addSliceTests() {
+	// Slice containing standard float32 values.
+	v := []float32{3.14, 6.28, 12.56}
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "float32"
+	vs := "{\n (" + vt + ") 3.14,\n (" + vt + ") 6.28,\n (" + vt + ") 12.56\n}"
+	addDumpTest(v, "([]"+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*[]"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**[]"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Slice containing type with custom formatter on pointer receiver only.
+	v2 := []pstringer{"1", "2", "3"}
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "spew_test.pstringer"
+	v2s := "{\n (" + v2t + ") stringer 1,\n (" + v2t + ") stringer 2,\n (" +
+		v2t + ") stringer 3\n}"
+	addDumpTest(v2, "([]"+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*[]"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**[]"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+}
+
+func addStringTests() {
+	// Standard string.
+	v := "test"
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "string"
+	vs := "\"test\""
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+}
+
+func addNilInterfaceTests() {
+	// Nil interface.
+	var v interface{}
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "interface {}"
+	vs := "<nil>"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+}
+
+func addMapTests() {
+	// Map with string keys and int vals.
+	v := map[string]int{"one": 1}
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "map[string]int"
+	vt1 := "string"
+	vt2 := "int"
+	vs := "{\n (" + vt1 + ") \"one\": (" + vt2 + ") 1\n}"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Map with custom formatter type on pointer receiver only keys and vals.
+	v2 := map[pstringer]pstringer{"one": "1"}
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "map[spew_test.pstringer]spew_test.pstringer"
+	v2t1 := "spew_test.pstringer"
+	v2t2 := "spew_test.pstringer"
+	v2s := "{\n (" + v2t1 + ") stringer one: (" + v2t2 + ") stringer 1\n}"
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+
+	// Map with interface keys and values.
+	v3 := map[interface{}]interface{}{"one": 1}
+	pv3 := &v3
+	v3Addr := fmt.Sprintf("%p", pv3)
+	pv3Addr := fmt.Sprintf("%p", &pv3)
+	v3t := "map[interface {}]interface {}"
+	v3t1 := "string"
+	v3t2 := "int"
+	v3s := "{\n (" + v3t1 + ") \"one\": (" + v3t2 + ") 1\n}"
+	addDumpTest(v3, "("+v3t+") "+v3s+"\n")
+	addDumpTest(pv3, "(*"+v3t+")("+v3Addr+")("+v3s+")\n")
+	addDumpTest(&pv3, "(**"+v3t+")("+pv3Addr+"->"+v3Addr+")("+v3s+")\n")
+}
+
+func addStructTests() {
+	// Struct with primitives.
+	type s1 struct {
+		a int8
+		b uint8
+	}
+	v := s1{127, 255}
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "spew_test.s1"
+	vt2 := "int8"
+	vt3 := "uint8"
+	vs := "{\n a: (" + vt2 + ") 127,\n b: (" + vt3 + ") 255\n}"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Struct that contains another struct.
+	type s2 struct {
+		s1 s1
+		b  bool
+	}
+	v2 := s2{s1{127, 255}, true}
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "spew_test.s2"
+	v2t2 := "spew_test.s1"
+	v2t3 := "int8"
+	v2t4 := "uint8"
+	v2t5 := "bool"
+	v2s := "{\n s1: (" + v2t2 + ") {\n  a: (" + v2t3 + ") 127,\n  b: (" +
+		v2t4 + ") 255\n },\n b: (" + v2t5 + ") true\n}"
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+
+	// Struct that contains custom type with Stringer pointer interface via both
+	// exported and unexported fields.
+	type s3 struct {
+		s pstringer
+		S pstringer
+	}
+	v3 := s3{"test", "test2"}
+	pv3 := &v3
+	v3Addr := fmt.Sprintf("%p", pv3)
+	pv3Addr := fmt.Sprintf("%p", &pv3)
+	v3t := "spew_test.s3"
+	v3t2 := "spew_test.pstringer"
+	v3s := "{\n s: (" + v3t2 + ") stringer test,\n S: (" + v3t2 +
+		") stringer test2\n}"
+	addDumpTest(v3, "("+v3t+") "+v3s+"\n")
+	addDumpTest(pv3, "(*"+v3t+")("+v3Addr+")("+v3s+")\n")
+	addDumpTest(&pv3, "(**"+v3t+")("+pv3Addr+"->"+v3Addr+")("+v3s+")\n")
+}
+
+func addUintptrTests() {
+	// Null pointer.
+	v := uintptr(0)
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "uintptr"
+	vs := "<nil>"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Address of real variable.
+	i := 1
+	v2 := uintptr(unsafe.Pointer(&i))
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "uintptr"
+	v2s := fmt.Sprintf("%p", &i)
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+}
+
+func addUnsafePointerTests() {
+	// Null pointer.
+	v := unsafe.Pointer(uintptr(0))
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "unsafe.Pointer"
+	vs := "<nil>"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Address of real variable.
+	i := 1
+	v2 := unsafe.Pointer(&i)
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "unsafe.Pointer"
+	v2s := fmt.Sprintf("%p", &i)
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+}
+
+func addChanTests() {
+	// Nil channel.
+	var v chan int
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "chan int"
+	vs := "<nil>"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Real channel.
+	v2 := make(chan int)
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "chan int"
+	v2s := fmt.Sprintf("%p", v2)
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+}
+
+func addFuncTests() {
+	// Function with no params and no returns.
+	v := addIntTests
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "func()"
+	vs := fmt.Sprintf("%p", v)
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs+")\n")
+
+	// Function with param and no returns.
+	v2 := TestDump
+	pv2 := &v2
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "func(*testing.T)"
+	v2s := fmt.Sprintf("%p", v2)
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s+")\n")
+
+	// Function with multiple params and multiple returns.
+	var v3 = func(i int, s string) (b bool, err error) {
+		return true, nil
+	}
+	pv3 := &v3
+	v3Addr := fmt.Sprintf("%p", pv3)
+	pv3Addr := fmt.Sprintf("%p", &pv3)
+	v3t := "func(int, string) (bool, error)"
+	v3s := fmt.Sprintf("%p", v3)
+	addDumpTest(v3, "("+v3t+") "+v3s+"\n")
+	addDumpTest(pv3, "(*"+v3t+")("+v3Addr+")("+v3s+")\n")
+	addDumpTest(&pv3, "(**"+v3t+")("+pv3Addr+"->"+v3Addr+")("+v3s+")\n")
+}
+
+func addCircularTests() {
+	// Struct that is circular through self referencing.
+	type circular struct {
+		c *circular
+	}
+	v := circular{nil}
+	v.c = &v
+	pv := &v
+	vAddr := fmt.Sprintf("%p", pv)
+	pvAddr := fmt.Sprintf("%p", &pv)
+	vt := "spew_test.circular"
+	vs := "{\n c: (*" + vt + ")(" + vAddr + ")({\n  c: (*" + vt + ")(" +
+		vAddr + ")(<already shown>)\n })\n}"
+	vs2 := "{\n c: (*" + vt + ")(" + vAddr + ")(<already shown>)\n}"
+	addDumpTest(v, "("+vt+") "+vs+"\n")
+	addDumpTest(pv, "(*"+vt+")("+vAddr+")("+vs2+")\n")
+	addDumpTest(&pv, "(**"+vt+")("+pvAddr+"->"+vAddr+")("+vs2+")\n")
+
+	// Structs that are circular through cross referencing.
+	v2 := xref1{nil}
+	ts2 := xref2{&v2}
+	v2.ps2 = &ts2
+	pv2 := &v2
+	ts2Addr := fmt.Sprintf("%p", &ts2)
+	v2Addr := fmt.Sprintf("%p", pv2)
+	pv2Addr := fmt.Sprintf("%p", &pv2)
+	v2t := "spew_test.xref1"
+	v2t2 := "spew_test.xref2"
+	v2s := "{\n ps2: (*" + v2t2 + ")(" + ts2Addr + ")({\n  ps1: (*" + v2t +
+		")(" + v2Addr + ")({\n   ps2: (*" + v2t2 + ")(" + ts2Addr +
+		")(<already shown>)\n  })\n })\n}"
+	v2s2 := "{\n ps2: (*" + v2t2 + ")(" + ts2Addr + ")({\n  ps1: (*" + v2t +
+		")(" + v2Addr + ")(<already shown>)\n })\n}"
+	addDumpTest(v2, "("+v2t+") "+v2s+"\n")
+	addDumpTest(pv2, "(*"+v2t+")("+v2Addr+")("+v2s2+")\n")
+	addDumpTest(&pv2, "(**"+v2t+")("+pv2Addr+"->"+v2Addr+")("+v2s2+")\n")
+
+	// Structs that are indirectly circular.
+	v3 := indirCir1{nil}
+	tic2 := indirCir2{nil}
+	tic3 := indirCir3{&v3}
+	tic2.ps3 = &tic3
+	v3.ps2 = &tic2
+	pv3 := &v3
+	tic2Addr := fmt.Sprintf("%p", &tic2)
+	tic3Addr := fmt.Sprintf("%p", &tic3)
+	v3Addr := fmt.Sprintf("%p", pv3)
+	pv3Addr := fmt.Sprintf("%p", &pv3)
+	v3t := "spew_test.indirCir1"
+	v3t2 := "spew_test.indirCir2"
+	v3t3 := "spew_test.indirCir3"
+	v3s := "{\n ps2: (*" + v3t2 + ")(" + tic2Addr + ")({\n  ps3: (*" + v3t3 +
+		")(" + tic3Addr + ")({\n   ps1: (*" + v3t + ")(" + v3Addr +
+		")({\n    ps2: (*" + v3t2 + ")(" + tic2Addr +
+		")(<already shown>)\n   })\n  })\n })\n}"
+	v3s2 := "{\n ps2: (*" + v3t2 + ")(" + tic2Addr + ")({\n  ps3: (*" + v3t3 +
+		")(" + tic3Addr + ")({\n   ps1: (*" + v3t + ")(" + v3Addr +
+		")(<already shown>)\n  })\n })\n}"
+	addDumpTest(v3, "("+v3t+") "+v3s+"\n")
+	addDumpTest(pv3, "(*"+v3t+")("+v3Addr+")("+v3s2+")\n")
+	addDumpTest(&pv3, "(**"+v3t+")("+pv3Addr+"->"+v3Addr+")("+v3s2+")\n")
+}
+
+// TestDump executes all of the tests described by dumpTests.
+func TestDump(t *testing.T) {
+	t.Logf("Running %d tests", len(dumpTests))
+	for i, test := range dumpTests {
+		buf := new(bytes.Buffer)
+		spew.Fdump(buf, test.in)
+		s := buf.String()
+		if test.want != buf.String() {
+			t.Errorf("Dump #%d\n got: %s want: %s", i, s, test.want)
+			continue
+		}
+	}
+}
+
+// Setup tests.f
+func init() {
+	addIntTests()
+	addUintTests()
+	addBoolTests()
+	addFloatTests()
+	addComplexTests()
+	addArrayTests()
+	addSliceTests()
+	addStringTests()
+	addNilInterfaceTests()
+	addMapTests()
+	addStructTests()
+	addUintptrTests()
+	addUnsafePointerTests()
+	addChanTests()
+	addFuncTests()
+	addCircularTests()
+}

spew/example_test.go

@@ -0,0 +1,132 @@
+/*
+ * Copyright (c) 2013 Dave Collins <dave@davec.name>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+package spew_test
+
+import (
+	"fmt"
+	"github.com/davecgh/go-spew/spew"
+)
+
+type Flag int
+
+const (
+	flagOne Flag = iota
+	flagTwo
+)
+
+var flagStrings = map[Flag]string{
+	flagOne: "flagOne",
+	flagTwo: "flagTwo",
+}
+
+func (f Flag) String() string {
+	if s, ok := flagStrings[f]; ok {
+		return s
+	}
+	return fmt.Sprintf("Unknown flag (%d)", int(f))
+}
+
+type Bar struct {
+	flag Flag
+	data uintptr
+}
+
+type Foo struct {
+	unexportedField Bar
+	ExportedField   map[interface{}]interface{}
+}
+
+// This example demonstrates how to use Dump to dump variables to stdout.
+func ExampleDump() {
+	// The following package level declarations are assumed for this example:
+	/*
+		type Flag int
+
+		const (
+			flagOne Flag = iota
+			flagTwo
+		)
+
+		var flagStrings = map[Flag]string{
+			flagOne: "flagOne",
+			flagTwo: "flagTwo",
+		}
+
+		func (f Flag) String() string {
+			if s, ok := flagStrings[f]; ok {
+				return s
+			}
+			return fmt.Sprintf("Unknown flag (%d)", int(f))
+		}
+
+		type Bar struct {
+			flag Flag
+			data uintptr
+		}
+
+		type Foo struct {
+			unexportedField Bar
+			ExportedField   map[interface{}]interface{}
+		}
+	*/
+
+	// Setup some sample data structures for the example.
+	bar := Bar{Flag(flagTwo), uintptr(0)}
+	s1 := Foo{bar, map[interface{}]interface{}{"one": true}}
+	f := Flag(5)
+
+	// Dump!
+	spew.Dump(s1, f)
+
+	// Output:
+	// (spew_test.Foo) {
+	//  unexportedField: (spew_test.Bar) {
+	//   flag: (spew_test.Flag) flagTwo,
+	//   data: (uintptr) <nil>
+	//  },
+	//  ExportedField: (map[interface {}]interface {}) {
+	//   (string) "one": (bool) true
+	//  }
+	// }
+	// (spew_test.Flag) Unknown flag (5)
+	//
+}
+
+// This example demonstrates how to use Printf to display a variable with a
+// format string and inline formatting.
+func ExamplePrintf() {
+	// Create a double pointer to a uint 8.
+	ui8 := uint8(5)
+	pui8 := &ui8
+	ppui8 := &pui8
+
+	// Create a circular data type.
+	type circular struct {
+		ui8 uint8
+		c   *circular
+	}
+	c := circular{ui8: 1}
+	c.c = &c
+
+	// Print!
+	spew.Printf("ppui8: %v\n", ppui8)
+	spew.Printf("circular: %v\n", c)
+
+	// Output:
+	// ppui8: <**>5
+	// circular: {1 <*>{1 <*><shown>}}
+}

spew/format.go

@@ -0,0 +1,338 @@
+/*
+ * Copyright (c) 2013 Dave Collins <dave@davec.name>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+package spew
+
+import (
+	"bytes"
+	"fmt"
+	"reflect"
+	"strconv"
+	"strings"
+)
+
+// supportedFlags is a list of all the character flags supported by fmt package.
+const supportedFlags = "0-+# "
+
+// formatState implements the fmt.Formatter interface and contains information
+// about the state of a formatting operation.  The NewFormatter function can
+// be used to get a new Formatter which can be used directly as arguments
+// in standard fmt package printing calls.
+type formatState struct {
+	value    interface{}
+	buffer   bytes.Buffer
+	depth    int
+	pointers map[uintptr]int // Holds map of points and depth they were seen at
+	fs       fmt.State
+}
+
+// buildDefaultFormat recreates the original format string without precision
+// and width information to pass in to fmt.Sprintf in the case of an
+// unrecognized type.  Unless new types are added to the language, this
+// function won't ever be called.
+func (f *formatState) buildDefaultFormat() (format string) {
+	buf := bytes.NewBuffer(percentBytes)
+
+	for _, flag := range supportedFlags {
+		if f.fs.Flag(int(flag)) {
+			buf.WriteRune(flag)
+		}
+	}
+
+	buf.WriteRune('v')
+
+	format = buf.String()
+	return format
+}
+
+// constructOrigFormat recreates the original format string including precision
+// and width information to pass along to the standard fmt package.  This allows
+// automatic deferral of all format strings this package doesn't support.
+func (f *formatState) constructOrigFormat(verb rune) (format string) {
+	buf := bytes.NewBuffer(percentBytes)
+
+	for _, flag := range supportedFlags {
+		if f.fs.Flag(int(flag)) {
+			buf.WriteRune(flag)
+		}
+	}
+
+	if width, ok := f.fs.Width(); ok {
+		buf.WriteString(strconv.Itoa(width))
+	}
+
+	if precision, ok := f.fs.Precision(); ok {
+		buf.Write(precisionBytes)
+		buf.WriteString(strconv.Itoa(precision))
+	}
+
+	buf.WriteRune(verb)
+
+	format = buf.String()
+	return format
+}
+
+// formatPtr handles formatting of pointers by indirecting them as necessary.
+func (f *formatState) formatPtr(v reflect.Value) {
+	// Display nil if top level poiner is nil.
+	if v.IsNil() {
+		f.buffer.Write(nilAngleBytes)
+		return
+	}
+
+	// Remove pointers at or below the current depth from map used to detect
+	// circular refs.
+	for k, depth := range f.pointers {
+		if depth >= f.depth {
+			delete(f.pointers, k)
+		}
+	}
+
+	plusSyntax := f.fs.Flag('+')
+
+	// Keep list of all dereferenced pointers to possibly show later.
+	pointerChain := make([]uintptr, 0)
+
+	// Figure out how many levels of indirection there are by derferencing
+	// pointers and unpacking interfaces down the chain while detecting circular
+	// references.
+	nilFound := false
+	cycleFound := false
+	indirects := 0
+	ve := v
+	for ve.Kind() == reflect.Ptr {
+		indirects++
+		if ve.IsNil() {
+			nilFound = true
+			break
+		}
+		addr := ve.Pointer()
+		pointerChain = append(pointerChain, addr)
+		if pd, ok := f.pointers[addr]; ok && pd < f.depth {
+			cycleFound = true
+			break
+		}
+		f.pointers[addr] = f.depth
+
+		ve = ve.Elem()
+		if ve.Kind() == reflect.Interface {
+			if ve.IsNil() {
+				nilFound = true
+				break
+			}
+			ve = ve.Elem()
+		}
+	}
+
+	// Display indirection level.
+	f.buffer.Write(openAngleBytes)
+	f.buffer.WriteString(strings.Repeat("*", indirects))
+	f.buffer.Write(closeAngleBytes)
+
+	// Display pointer information depending on flags.
+	if plusSyntax && (len(pointerChain) > 0) {
+		f.buffer.Write(openParenBytes)
+		for i, addr := range pointerChain {
+			if i > 0 {
+				f.buffer.Write(pointerChainBytes)
+			}
+			printHexPtr(&f.buffer, addr)
+		}
+		f.buffer.Write(closeParenBytes)
+	}
+
+	// Display dereferenced value.
+	switch {
+	case nilFound == true:
+		f.buffer.Write(nilAngleBytes)
+
+	case cycleFound == true:
+		f.buffer.Write(circularShortBytes)
+
+	default:
+		f.format(ve)
+	}
+}
+
+// format is the main workhorse for providing the Formatter interface.  It
+// uses the passed reflect value to figure out what kind of object we are
+// dealing with and formats it appropriately.  It is a recursive function,
+// however circular data structures are detected and handled properly.
+func (f *formatState) format(v reflect.Value) {
+	// Call error/Stringer interfaces if they exist and the handle methods
+	// flag is enabled.
+	kind := v.Kind()
+	if !Config.DisableMethods {
+		if (kind != reflect.Invalid) && (kind != reflect.Interface) {
+			if handled := handleMethods(&f.buffer, v); handled {
+				return
+			}
+		}
+	}
+
+	switch kind {
+	case reflect.Invalid:
+		f.buffer.Write(invalidAngleBytes)
+
+	case reflect.Bool:
+		printBool(&f.buffer, v.Bool())
+
+	case reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Int:
+		printInt(&f.buffer, v.Int())
+
+	case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uint:
+		printUint(&f.buffer, v.Uint())
+
+	case reflect.Float32:
+		printFloat(&f.buffer, v.Float(), 32)
+
+	case reflect.Float64:
+		printFloat(&f.buffer, v.Float(), 64)
+
+	case reflect.Complex64:
+		printComplex(&f.buffer, v.Complex(), 32)
+
+	case reflect.Complex128:
+		printComplex(&f.buffer, v.Complex(), 64)
+
+	case reflect.Array, reflect.Slice:
+		f.buffer.WriteRune('[')
+		f.depth++
+		if (Config.MaxDepth != 0) && (f.depth > Config.MaxDepth) {
+			f.buffer.Write(maxShortBytes)
+		} else {
+			numEntries := v.Len()
+			for i := 0; i < numEntries; i++ {
+				if i > 0 {
+					f.buffer.WriteRune(' ')
+				}
+				f.format(unpackValue(v.Index(i)))
+			}
+		}
+		f.depth--
+		f.buffer.WriteRune(']')
+
+	case reflect.String:
+		f.buffer.WriteString(v.String())
+
+	case reflect.Interface:
+		// Do nothing.  We should never get here due to unpackValue calls
+
+	case reflect.Map:
+		f.buffer.Write(openMapBytes)
+		f.depth++
+		if (Config.MaxDepth != 0) && (f.depth > Config.MaxDepth) {
+			f.buffer.Write(maxShortBytes)
+		} else {
+			keys := v.MapKeys()
+			for i, key := range keys {
+				if i > 0 {
+					f.buffer.WriteRune(' ')
+				}
+				f.format(unpackValue(key))
+				f.buffer.WriteRune(':')
+				f.format(unpackValue(v.MapIndex(key)))
+			}
+		}
+		f.depth--
+		f.buffer.Write(closeMapBytes)
+
+	case reflect.Ptr:
+		f.formatPtr(v)
+
+	case reflect.Struct:
+		numFields := v.NumField()
+		f.buffer.WriteRune('{')
+		f.depth++
+		if (Config.MaxDepth != 0) && (f.depth > Config.MaxDepth) {
+			f.buffer.Write(maxShortBytes)
+		} else {
+			vt := v.Type()
+			for i := 0; i < numFields; i++ {
+				if i > 0 {
+					f.buffer.WriteRune(' ')
+				}
+				vtf := vt.Field(i)
+				if f.fs.Flag('+') {
+					f.buffer.WriteString(vtf.Name)
+					f.buffer.WriteRune(':')
+				}
+				f.format(unpackValue(v.Field(i)))
+			}
+		}
+		f.depth--
+		f.buffer.WriteRune('}')
+
+	case reflect.Uintptr:
+		printHexPtr(&f.buffer, uintptr(v.Uint()))
+
+	case reflect.UnsafePointer, reflect.Chan, reflect.Func:
+		printHexPtr(&f.buffer, v.Pointer())
+
+	// There were not any other types at the time this code was written, but
+	// fall back to letting the default fmt package handle it if any get added.
+	default:
+		format := f.buildDefaultFormat()
+		if v.CanInterface() {
+			f.buffer.WriteString(fmt.Sprintf(format, v.Interface()))
+		} else {
+			f.buffer.WriteString(fmt.Sprintf(format, v.String()))
+		}
+	}
+}
+
+// Format satisfies the fmt.Formatter interface. See NewFormatter for usage
+// details.
+func (f *formatState) Format(fs fmt.State, verb rune) {
+	f.fs = fs
+
+	// Use standard formatting for verbs that are not v or #v.
+	if (verb != 'v') || (verb == 'v' && fs.Flag('#')) {
+		format := f.constructOrigFormat(verb)
+		fmt.Fprintf(fs, format, f.value)
+		return
+	}
+
+	if f.value == nil {
+		fmt.Fprint(fs, string(nilAngleBytes))
+		return
+	}
+
+	f.format(reflect.ValueOf(f.value))
+	f.buffer.WriteTo(fs)
+}
+
+/*
+NewFormatter returns a custom formatter that satisfies the fmt.Formatter
+interface.  As a result, it integrates cleanly with standard fmt package
+printing functions.  The formatter is useful for inline printing of smaller data
+types similar to the standard %v format specifier.
+
+The custom formatter only responds to the %v and %+v verb combinations.  Any
+other variations such as %x, %q, and %#v will be sent to the the standard fmt
+package for formatting.  In addition, the custom formatter ignores the width and
+precision arguments (however they will still work on the format specifiers not
+handled by the custom formatter).
+
+Typically this function shouldn't be called directly.  It is much easier to make
+use of the custom formatter is to call one of the convenience functions such as
+Printf, Println, or Printf.
+*/
+func NewFormatter(v interface{}) (f fmt.Formatter) {
+	fs := &formatState{value: v}
+	fs.pointers = make(map[uintptr]int)
+	return fs
+}

spew/spew.go

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2013 Dave Collins <dave@davec.name>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+package spew
+
+import (
+	"fmt"
+	"io"
+)
+
+// Errorf is a wrapper for fmt.Errorf that treats each argument as if it were
+// passed with a default Formatter interface returned by NewFormatter.  It
+// returns the formatted string as a value that satisfies error.  See
+// NewFormatter for formatting details.
+//
+// This function is shorthand for the following syntax:
+//
+//	fmt.Errorf(format, spew.NewFormatter(a), spew.NewFormatter(b))
+func Errorf(format string, a ...interface{}) (err error) {
+	return fmt.Errorf(format, convertArgs(a)...)
+}
+
+// Fprint is a wrapper for fmt.Fprint that treats each argument as if it were
+// passed with a default Formatter interface returned by NewFormatter.  It
+// returns the number of bytes written and any write error encountered.  See
+// NewFormatter for formatting details.
+//
+// This function is shorthand for the following syntax:
+//
+//	fmt.Fprint(w, spew.NewFormatter(a), spew.NewFormatter(b))
+func Fprint(w io.Writer, a ...interface{}) (n int, err error) {
+	return fmt.Fprint(w, convertArgs(a)...)
+}
+
+// Fprintf is a wrapper for fmt.Fprintf that treats each argument as if it were
+// passed with a default Formatter interface returned by NewFormatter.  It
+// returns the number of bytes written and any write error encountered.  See
+// NewFormatter for formatting details.
+//
+// This function is shorthand for the following syntax:
+//
+//	fmt.Fprintf(w, format, spew.NewFormatter(a), spew.NewFormatter(b))
+func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error) {
+	return fmt.Fprintf(w, format, convertArgs(a)...)
+}
+
+// Fprintln is a wrapper for fmt.Fprintln that treats each argument as if it
+// passed with a default Formatter interface returned by NewFormatter.  See
+// NewFormatter for formatting details.
+//
+// This function is shorthand for the following syntax:
+//
+//	fmt.Fprintln(w, spew.NewFormatter(a), spew.NewFormatter(b))
+func Fprintln(w io.Writer, a ...interface{}) (n int, err error) {
+	return fmt.Fprintln(w, convertArgs(a)...)
+}
+
+// Print is a wrapper for fmt.Print that treats each argument as if it were
+// passed with a default Formatter interface returned by NewFormatter.  It
+// returns the number of bytes written and any write error encountered.  See
+// NewFormatter for formatting details.
+//
+// This function is shorthand for the following syntax:
+//
+//	fmt.Print(spew.NewFormatter(a), spew.NewFormatter(b))
+func Print(a ...interface{}) (n int, err error) {
+	return fmt.Print(convertArgs(a)...)
+}
+
+// Printf is a wrapper for fmt.Printf that treats each argument as if it were
+// passed with a default Formatter interface returned by NewFormatter.  It
+// returns the number of bytes written and any write error encountered.  See
+// NewFormatter for formatting details.
+//
+// This function is shorthand for the following syntax:
+//
+//	fmt.Printf(format, spew.NewFormatter(a), spew.NewFormatter(b))
+func Printf(format string, a ...interface{}) (n int, err error) {
+	return fmt.Printf(format, convertArgs(a)...)
+}
+
+// Println is a wrapper for fmt.Println that treats each argument as if it were
+// passed with a default Formatter interface returned by NewFormatter.  It
+// returns the number of bytes written and any write error encountered.  See
+// NewFormatter for formatting details.
+//
+// This function is shorthand for the following syntax:
+//
+//	fmt.Println(spew.NewFormatter(a), spew.NewFormatter(b))
+func Println(a ...interface{}) (n int, err error) {
+	return fmt.Println(convertArgs(a)...)
+}
+
+// convertArgs accepts a slice of arguments and returns a slice of the same
+// length with each argument converted to a default spew Formatter interface.
+func convertArgs(args []interface{}) (formatters []interface{}) {
+	formatters = make([]interface{}, len(args))
+	for index, arg := range args {
+		formatters[index] = NewFormatter(arg)
+	}
+	return formatters
+}