map_slice.go

package pipe

import (
	"fmt"
	"reflect"
)

// MapSlice is of type: func(fn func(T) U, input []T) []U.
// It returns a slice of fn(item) for each item in input.
func MapSlice(fn, input interface{}) interface{} {
	checkMapFuncType(fn, input)

	inputValue := reflect.ValueOf(input)
	fnValue := reflect.ValueOf(fn)

	if inputValue.Kind() != reflect.Slice &&
		inputValue.Kind() != reflect.Array {
		panic(fmt.Sprintf("MapSlice called on invalid type: %s", inputValue.Type()))
	}

	outputType := reflect.SliceOf(fnValue.Type().Out(0))
	output := reflect.MakeSlice(outputType, 0, inputValue.Len())

	for i := 0; i < inputValue.Len(); i++ {
		output = reflect.Append(
			output,
			fnValue.Call([]reflect.Value{inputValue.Index(i)})[0],
		)
	}

	return output.Interface()
}