# README

messagediff

A library for doing diffs of arbitrary Golang structs.

If the unsafe package is available messagediff will diff unexported fields in addition to exported fields. This is primarily used for testing purposes as it allows for providing informative error messages.

Optionally, fields in structs can be tagged as testdiff:"ignore" to make messagediff skip it when doing the comparison.

Example Usage

In a normal file:

package main

import "gopkg.in/d4l3k/messagediff.v1"

type someStruct struct {
    A, b int
    C []int
}

func main() {
    a := someStruct{1, 2, []int{1}}
    b := someStruct{1, 3, []int{1, 2}}
    diff, equal := messagediff.PrettyDiff(a, b)
    /*
        diff =
        `added: .C[1] = 2
        modified: .b = 3`

        equal = false
    */
}

In a test:

import "gopkg.in/d4l3k/messagediff.v1"

...

type someStruct struct {
    A, b int
    C []int
}

func TestSomething(t *testing.T) {
    want := someStruct{1, 2, []int{1}}
    got := someStruct{1, 3, []int{1, 2}}
    if diff, equal := messagediff.PrettyDiff(want, got); !equal {
        t.Errorf("Something() = %#v\n%s", got, diff)
    }
}

To ignore a field in a struct, just annotate it with testdiff:"ignore" like this:

package main

import "gopkg.in/d4l3k/messagediff.v1"

type someStruct struct {
    A int
    B int `testdiff:"ignore"`
}

func main() {
    a := someStruct{1, 2}
    b := someStruct{1, 3}
    diff, equal := messagediff.PrettyDiff(a, b)
    /*
        equal = true
        diff = ""
    */
}

See the DeepDiff function for using the diff results programmatically.