builtin: add Append()

Author: joonas-fi

builtin/builtin.go

@@ -80,3 +80,9 @@ func Must[T any](value T, err error) T {
 func FirstError(errs ...error) error {
 	return FirstNonEmpty(errs...)
 }
+
+
+// append to a slice without needing the "assign to same variable" boilerplate
+func Append[T any](slice *[]T, item T) {
+	*slice = append(*slice, item)
+}

builtin/builtin_test.go

@@ -3,6 +3,7 @@ package builtin
 import (
 	"context"
 	"errors"
+	"strings"
 	"testing"
 
 	"github.com/function61/gokit/testing/assert"
@@ -76,3 +77,12 @@ func TestFirstNonEmptyWithError(t *testing.T) {
 	assert.EqualString(t, FirstNonEmpty(nilError, actualError).Error(), "actual")
 	assert.Assert(t, FirstNonEmpty(nilError, nilError) == nil)
 }
+
+func TestAppend(t *testing.T) {
+	favoriteThings := []string{"hamburger"}
+
+	Append(&favoriteThings, "food")
+	Append(&favoriteThings, "bar")
+
+	assert.EqualString(t, strings.Join(favoriteThings, ", "), "hamburger, food, bar")
+}