proposal: golang.org/x/exp/slices: Add "Merge"

[6543]

As append(append(append(a, b...), c...), d...) is way to common :/

I propose a function that gets a list of slices of same type and return one slice of that type*

// Merge return a new slice that combines all values of input slices
func Merge[T any](slices ...[]T) []T {
	sl := 0
	for i := range slices {
		sl += len(slices[i])
	}
	result := make([]T, sl)
	cp := 0
	for _, s := range slices {
		if sLen := len(s); sLen != 0 {
			copy(result[cp:], s)
			cp += sLen
		}
	}
	return result
}

test:

	resultSS := MergeSlices([]string{}, []string{"a", "b"}, []string{"c"}, nil)
	assert.EqualValues(t, []string{"a", "b", "c"}, resultSS)

	resultIS := MergeSlices([]int{}, []int{1, 2}, []int{4}, nil)
	assert.EqualValues(t, []int{1, 2, 4}, resultIS)

[6543]

If it will get accepted I'll file a pull :)

[ericlagergren]

Dupe of #56353

[seankhliao]

Duplicate of #56353