go-spew

Go-spew implements a deep pretty printer for Go data structures to aid in debugging. It is still under initial development, so some of the formatting output is likely to change, however it is already quite capable. It is licensed under the liberal ISC license, so it may be used in open source or commercial projects.

If you're interested in reading about how this package came to life and some of the challenges involved in provide a deep pretty printer, there is a blog post about it here.

Documentation

Full go doc style documentation for the project can be viewed online without installing this package by using the excellent GoDoc site here: http://godoc.org/github.com/davecgh/go-spew/spew

You can also view the documentation locally once the package is installed with the godoc tool by running godoc -http=":6060" and pointing your browser to http://localhost:6060/pkg/github.com/davecgh/go-spew/spew

Installation

$ go get github.com/davecgh/go-spew/spew

Quick Start

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 %v (most compact), %+v (adds pointer addresses), %#v (adds types), or %#+v (adds types and pointer addresses):

spew.Printf("myVar1: %v -- myVar2: %+v", myVar1, myVar2)
spew.Printf("myVar3: %#v -- myVar4: %#+v", myVar3, myVar4)
spew.Fprintf(someWriter, "myVar1: %v -- myVar2: %+v", myVar1, myVar2)
spew.Fprintf(someWriter, "myVar3: %#v -- myVar4: %#+v", myVar3, myVar4)

Sample Dump Output

(main.Foo) {
 unexportedField: (*main.Bar)(0xf84002e210)({
  flag: (main.Flag) flagTwo,
  data: (uintptr) <nil>
 }),
 ExportedField: (map[interface {}]interface {}) {
  (string) "one": (bool) true
 }
}

Sample Formatter Output

Double pointer to a uint8:

	  %v: <**>5
	 %+v: <**>(0xf8400420d0->0xf8400420c8)5
	 %#v: (**uint8)5
	%#+v: (**uint8)(0xf8400420d0->0xf8400420c8)5

Pointer to circular struct with a uint8 field and a pointer to itself:

	  %v: <*>{1 <*><shown>}
	 %+v: <*>(0xf84003e260){ui8:1 c:<*>(0xf84003e260)<shown>}
	 %#v: (*main.circular){ui8:(uint8)1 c:(*main.circular)<shown>}
	%#+v: (*main.circular)(0xf84003e260){ui8:(uint8)1 c:(*main.circular)(0xf84003e260)<shown>}

Configuration Options

Configuration of spew is handled by fields in the ConfigState type. For convenience, all of the top-level functions use a global state available via the spew.Config global.

It is also possible to create a ConfigState instance that provides methods equivalent to the top-level functions. This allows concurrent configuration options. See the ConfigState documentation for more details.

* Indent
	String to use for each indentation level for Dump functions.
	It is a single space by default.  A popular alternative is "\t".

* MaxDepth
	Maximum number of levels to descend into nested data structures.
	There is no limit by default.

* DisableMethods
	Disables invocation of error and Stringer interface methods.
	Method invocation is enabled by default.

* 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.

License

Go-spew is licensed under the liberal ISC License.