less.go

package permutation

import (
	"errors"
	"reflect"
)

// Less defines the comparison function that can be used to sort a list
type Less func(left, right interface{}) bool

func getLessFunctionByValueType(value reflect.Value) (Less, error) {
	switch value.Type().Elem().Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return lessInt, nil
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		return lessUint, nil
	case reflect.Float32, reflect.Float64:
		return lessFloat, nil
	case reflect.String:
		return lessString, nil
	default:
		return nil, errors.New("the element type of slice is not ordered, you must provide a function")
	}
}

func lessUint(left, right interface{}) bool {
	return reflect.ValueOf(left).Uint() < reflect.ValueOf(right).Uint()
}

func lessInt(left, right interface{}) bool {
	return reflect.ValueOf(left).Int() < reflect.ValueOf(right).Int()
}

func lessFloat(left, right interface{}) bool {
	return reflect.ValueOf(left).Float() < reflect.ValueOf(right).Float()
}

func lessString(left, right interface{}) bool {
	return reflect.ValueOf(left).Interface().(string) < reflect.ValueOf(right).Interface().(string)
}