Add a Concat slice function.

This is a variadic wrapper around Flatten that allows callers
to assemble one slice from many slices without first joining
them into a slice-of-slices.

Author: FGasper

slice.go

@@ -261,6 +261,7 @@ func PartitionBy[T any, K comparable, Slice ~[]T](collection Slice, iteratee fun
 }
 
 // Flatten returns a slice a single level deep.
+// See also: Concat
 // Play: https://go.dev/play/p/rbp9ORaMpjw
 func Flatten[T any, Slice ~[]T](collection []Slice) Slice {
 	totalLen := 0
@@ -276,6 +277,12 @@ func Flatten[T any, Slice ~[]T](collection []Slice) Slice {
 	return result
 }
 
+// Concat assembles >=1 slice’s members into a single slice.
+// See also: Flatten, Union.
+func Concat[T any, Slice ~[]T](collections ...Slice) Slice {
+	return Flatten(collections)
+}
+
 // Interleave round-robin alternating input slices and sequentially appending value at index into result.
 // Play: https://go.dev/play/p/-RJkTLQEDVt
 func Interleave[T any, Slice ~[]T](collections ...Slice) Slice {

slice_test.go

@@ -357,6 +357,20 @@ func TestFlatten(t *testing.T) {
 	is.IsType(nonempty, allStrings, "type preserved")
 }
 
+func TestConcat(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	result1 := Concat([][]int{{0, 1}, {2, 3, 4, 5}}...)
+
+	is.Equal(result1, []int{0, 1, 2, 3, 4, 5})
+
+	type myStrings []string
+	allStrings := myStrings{"", "foo", "bar"}
+	nonempty := Concat([]myStrings{allStrings}...)
+	is.IsType(nonempty, allStrings, "type preserved")
+}
+
 func TestInterleave(t *testing.T) {
 	t.Parallel()
 	is := assert.New(t)