Checking the equality of two slices

Question

How can I check if two slices are equal?

Answer 1

You need to loop over each of the elements in the slice and test. Equality for slices is not defined. However, there is a bytes.Equal function if you are comparing values of type []byte.

func testEq(a, b []Type) bool {

    // If one is nil, the other must also be nil.
    if (a == nil) != (b == nil) { 
        return false; 
    }

    if len(a) != len(b) {
        return false
    }

    for i := range a {
        if a[i] != b[i] {
            return false
        }
    }

    return true
}

Answer 2

You should use reflect.DeepEqual()

DeepEqual is a recursive relaxation of Go's == operator.

DeepEqual reports whether x and y are “deeply equal,” defined as follows. Two values of identical type are deeply equal if one of the following cases applies. Values of distinct types are never deeply equal.

Array values are deeply equal when their corresponding elements are deeply equal.

Struct values are deeply equal if their corresponding fields, both exported and unexported, are deeply equal.

Func values are deeply equal if both are nil; otherwise they are not deeply equal.

Interface values are deeply equal if they hold deeply equal concrete values.

Map values are deeply equal if they are the same map object or if they have the same length and their corresponding keys (matched using Go equality) map to deeply equal values.

Pointer values are deeply equal if they are equal using Go's == operator or if they point to deeply equal values.

Slice values are deeply equal when all of the following are true: they are both nil or both non-nil, they have the same length, and either they point to the same initial entry of the same underlying array (that is, &x[0] == &y[0]) or their corresponding elements (up to length) are deeply equal. Note that a non-nil empty slice and a nil slice (for example, []byte{} and []byte(nil)) are not deeply equal.

Other values - numbers, bools, strings, and channels - are deeply equal if they are equal using Go's == operator.

Answer 3

This is just example using reflect.DeepEqual() that is given in @VictorDeryagin's answer.

package main

import (
    "fmt"
    "reflect"
)

func main() {
    a := []int {4,5,6}
    b := []int {4,5,6}
    c := []int {4,5,6,7}

    fmt.Println(reflect.DeepEqual(a, b))
    fmt.Println(reflect.DeepEqual(a, c))

}

Result:

true
false

Try it in Go Playground

Answer 4

If you have two []byte, compare them using bytes.Equal. The Golang documentation says:

Equal returns a boolean reporting whether a and b are the same length and contain the same bytes. A nil argument is equivalent to an empty slice.

Usage:

package main

import (
    "fmt"
    "bytes"
)

func main() {
    a := []byte {1,2,3}
    b := []byte {1,2,3}
    c := []byte {1,2,2}

    fmt.Println(bytes.Equal(a, b))
    fmt.Println(bytes.Equal(a, c))
}

This will print

true
false

Answer 5

In case that you are interested in writing a test, then github.com/stretchr/testify/assert is your friend.

Import the library at the very beginning of the file:

import (
    "github.com/stretchr/testify/assert"
)

Then inside the test you do:

func TestEquality_SomeSlice (t * testing.T) {
    a := []int{1, 2}
    b := []int{2, 1}
    assert.Equal(t, a, b)
}

The error prompted will be:

                Diff:
                --- Expected
                +++ Actual
                @@ -1,4 +1,4 @@
                 ([]int) (len=2) {
                + (int) 1,
                  (int) 2,
                - (int) 2,
                  (int) 1,
Test:           TestEquality_SomeSlice

Answer 6

And for now, here is https://github.com/google/go-cmp which

is intended to be a more powerful and safer alternative to reflect.DeepEqual for comparing whether two values are semantically equal.

package main

import (
    "fmt"

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

func main() {
    a := []byte{1, 2, 3}
    b := []byte{1, 2, 3}

    fmt.Println(cmp.Equal(a, b)) // true
}