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// Copyright 2017, The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package function provides functionality for identifying function types.
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package function
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import (
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	"reflect"
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	"regexp"
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	"runtime"
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	"strings"
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)
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type funcType int
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const (
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	_ funcType = iota
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	tbFunc  // func(T) bool
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	ttbFunc // func(T, T) bool
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	ttiFunc // func(T, T) int
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	trbFunc // func(T, R) bool
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	tibFunc // func(T, I) bool
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	trFunc  // func(T) R
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	Equal             = ttbFunc // func(T, T) bool
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	EqualAssignable   = tibFunc // func(T, I) bool; encapsulates func(T, T) bool
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	Transformer       = trFunc  // func(T) R
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	ValueFilter       = ttbFunc // func(T, T) bool
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	Less              = ttbFunc // func(T, T) bool
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	Compare           = ttiFunc // func(T, T) int
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	ValuePredicate    = tbFunc  // func(T) bool
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	KeyValuePredicate = trbFunc // func(T, R) bool
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)
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var boolType = reflect.TypeOf(true)
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var intType = reflect.TypeOf(0)
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// IsType reports whether the reflect.Type is of the specified function type.
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func IsType(t reflect.Type, ft funcType) bool {
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	if t == nil || t.Kind() != reflect.Func || t.IsVariadic() {
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		return false
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	}
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	ni, no := t.NumIn(), t.NumOut()
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	switch ft {
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	case tbFunc: // func(T) bool
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		if ni == 1 && no == 1 && t.Out(0) == boolType {
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			return true
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		}
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	case ttbFunc: // func(T, T) bool
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		if ni == 2 && no == 1 && t.In(0) == t.In(1) && t.Out(0) == boolType {
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			return true
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		}
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	case ttiFunc: // func(T, T) int
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		if ni == 2 && no == 1 && t.In(0) == t.In(1) && t.Out(0) == intType {
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			return true
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		}
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	case trbFunc: // func(T, R) bool
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		if ni == 2 && no == 1 && t.Out(0) == boolType {
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			return true
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		}
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	case tibFunc: // func(T, I) bool
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		if ni == 2 && no == 1 && t.In(0).AssignableTo(t.In(1)) && t.Out(0) == boolType {
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			return true
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		}
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	case trFunc: // func(T) R
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		if ni == 1 && no == 1 {
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			return true
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		}
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	}
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	return false
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}
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var lastIdentRx = regexp.MustCompile(`[_\p{L}][_\p{L}\p{N}]*$`)
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// NameOf returns the name of the function value.
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func NameOf(v reflect.Value) string {
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	fnc := runtime.FuncForPC(v.Pointer())
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	if fnc == nil {
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		return "<unknown>"
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	}
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	fullName := fnc.Name() // e.g., "long/path/name/mypkg.(*MyType).(long/path/name/mypkg.myMethod)-fm"
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	// Method closures have a "-fm" suffix.
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	fullName = strings.TrimSuffix(fullName, "-fm")
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	var name string
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	for len(fullName) > 0 {
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		inParen := strings.HasSuffix(fullName, ")")
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		fullName = strings.TrimSuffix(fullName, ")")
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		s := lastIdentRx.FindString(fullName)
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		if s == "" {
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			break
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		}
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		name = s + "." + name
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		fullName = strings.TrimSuffix(fullName, s)
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		if i := strings.LastIndexByte(fullName, '('); inParen && i >= 0 {
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			fullName = fullName[:i]
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		}
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		fullName = strings.TrimSuffix(fullName, ".")
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	}
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	return strings.TrimSuffix(name, ".")
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}
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