How to semantically compare structs vs nested slices regardless of order of elements in Go

How to semantically compare structures vs. nested slices regardless of the order of elements in Go is a common question. In the Go language, a structure is an aggregate data type, while a slice is a dynamic array. PHP editor Zimo will answer this question for you. When comparing structures, they are comparable only if all members are of comparable types. When comparing nested slices, we need to compare the elements in the slices level by level. If the element types of the slice are not comparable, we need to use a recursive method to compare each element of the slice. Whether it's a struct or a nested slice, we can compare elements by iterating over them.

Question content

Give the next type structure definition:

type A struct {
    Id  int
    Bs  []B
    Sub C
}

type B struct {
    Id  int
    Str string
}

type C struct {
    Id int
    Ds []D
}

type D struct {
    Id  int
    Num int
}

I want to test whether the next two instances of A are semantically equal regardless of the order of the slice elements in all hierarchy levels.

var want = &A{
    Id: 1,
    Bs: []B{{Id: 10, Str: "b10"}, {Id: 20, Str: "b20"}},
    Sub: C{
        Id: 100,
        Ds: []D{{Id: 101, Num: 1001}, {Id: 102, Num: 1002}},
    },
}

var got = &A{
    Id: 1,
    Bs: []B{{Id: 20, Str: "b20"}, {Id: 10, Str: "b10"}},
    Sub: C{
        Id: 100,
        Ds: []D{{Id: 102, Num: 1002}, {Id: 101, Num: 1001}},
    },
}

Assert comparison should return true

Workaround

Package cmp aims to be an update to reflect.DeepEqual Powerful, safer alternative for comparing two values ​​for semantic equality.

Here is a complete implementation of semantic equality structural comparison, regardless of the order of slice elements at all hierarchy levels.

File source.go

package main

type A struct {
    Id  int
    Bs  []B
    Sub C
}

type B struct {
    Id  int
    Str string
}

type C struct {
    Id int
    Ds []D
}

type D struct {
    Id  int
    Num int
}

func NewA() *A {
    return &A{
        Id: 1,
        Bs: []B{{Id: 20, Str: "b20"}, {Id: 10, Str: "b10"}},
        Sub: C{
            Id: 100,
            Ds: []D{{Id: 102, Num: 1002}, {Id: 101, Num: 1001}},
        },
    }
}

File source_test.go

package main

import (
    "fmt"
    "testing"

    "github.com/google/go-cmp/cmp"
    "github.com/google/go-cmp/cmp/cmpopts"
)

var want = &A{
    Id: 1,
    Bs: []B{{Id: 10, Str: "b10"}, {Id: 20, Str: "b20"}},
    Sub: C{
        Id: 100,
        Ds: []D{{Id: 101, Num: 1001}, {Id: 102, Num: 1002}},
    },
}

func TestNewA(t *testing.T) {
    got := NewA()
    less := func(x, y any) bool {
        switch xv := x.(type) {
        case B:
            yv := y.(B)
            return fmt.Sprintf("%d-%s", xv.Id, xv.Str) < fmt.Sprintf("%d-%s", yv.Id, yv.Str)
        case D:
            yv := y.(D)
            return fmt.Sprintf("%d-%d", xv.Id, xv.Num) < fmt.Sprintf("%d-%d", yv.Id, yv.Num)
        default:
            return false
        }
    }
    if diff := cmp.Diff(want, got, cmpopts.SortSlices(less)); diff != "" {
        t.Errorf("mismatch:\n%s", diff)
    }
}

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