1// Copyright 2017, The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE.md file.
4
5// Package function identifies function types.
6package function
7
8import "reflect"
9
10type funcType int
11
12const (
13	_ funcType = iota
14
15	ttbFunc // func(T, T) bool
16	tibFunc // func(T, I) bool
17	trFunc  // func(T) R
18
19	Equal           = ttbFunc // func(T, T) bool
20	EqualAssignable = tibFunc // func(T, I) bool; encapsulates func(T, T) bool
21	Transformer     = trFunc  // func(T) R
22	ValueFilter     = ttbFunc // func(T, T) bool
23	Less            = ttbFunc // func(T, T) bool
24)
25
26var boolType = reflect.TypeOf(true)
27
28// IsType reports whether the reflect.Type is of the specified function type.
29func IsType(t reflect.Type, ft funcType) bool {
30	if t == nil || t.Kind() != reflect.Func || t.IsVariadic() {
31		return false
32	}
33	ni, no := t.NumIn(), t.NumOut()
34	switch ft {
35	case ttbFunc: // func(T, T) bool
36		if ni == 2 && no == 1 && t.In(0) == t.In(1) && t.Out(0) == boolType {
37			return true
38		}
39	case tibFunc: // func(T, I) bool
40		if ni == 2 && no == 1 && t.In(0).AssignableTo(t.In(1)) && t.Out(0) == boolType {
41			return true
42		}
43	case trFunc: // func(T) R
44		if ni == 1 && no == 1 {
45			return true
46		}
47	}
48	return false
49}
50