concat.go

package main

import (
	"fmt"
	"reflect"
)

// concat returns a slice of type t that contains the specified items.
// Each item is appended according to its type: if it has type t, it is
// appended; if it is a slice of values of type t, each of its elements
// is appended; values of other types are ignored.
func concat(t reflect.Type, items ...interface{}) interface{} {
	out := reflect.MakeSlice(reflect.SliceOf(t), 0, len(items))
	for _, item := range items {
		v := reflect.ValueOf(item)
		if v.Kind() == t.Kind() {
			out = reflect.Append(out, v)
		} else if v.Kind() == reflect.Slice && v.Type().Elem().Kind() == t.Kind() {
			out = reflect.AppendSlice(out, v)
		}
	}
	return out.Interface()
}

func main() {
	a := "foo"
	b := []string{"bar", "baz"}
	c := ([]string)(nil)
	d := "qux"
	fmt.Printf("%#v\n", concat(reflect.TypeOf(a), a, b, c, d))
	// Output: []string{"foo", "bar", "baz", "qux"}
}