# README

messagediff

A library for doing diffs of arbitrary Golang structs. Fork of d4l3k/messagediff. Go-moduled, more options.

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.

Options:

fields in structs can be tagged as testdiff:"ignore" to make messagediff skip it when doing the comparison (see example).
fields can also be ignored by passing an option: PrettyDiff(a, b, IgnoreStructField("X"), ...)
ignore the differences in empty slices and nil slices. PrettyDiff(a, b, SliceWeakEmptyOption{}, ...)

Example Usage

package main

import "github.com/protolambda/messagediff"

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, from = 2; to = 3`

        equal = false
    */
}

Test usage example

import "github.com/protolambda/messagediff"

...

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("Unexpected difference in something: %s", got, diff)
    }
}

Ignore struct field with tag

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

package main

import "github.com/protolambda/messagediff"

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.