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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// MakeFunc implementation.
package reflect
import (
// makeFuncImpl is the closure value implementing the function
// returned by MakeFunc.
type makeFuncImpl struct {
// These first three words are layed out like ffi_go_closure.
code uintptr
ffi_cif unsafe.Pointer
ffi_fun func(unsafe.Pointer, unsafe.Pointer)
typ *funcType
fn func([]Value) []Value
// For gccgo we use the same entry point for functions and for
// method values.
method int
rcvr Value
// MakeFunc returns a new function of the given Type
// that wraps the function fn. When called, that new function
// does the following:
// - converts its arguments to a slice of Values.
// - runs results := fn(args).
// - returns the results as a slice of Values, one per formal result.
// The implementation fn can assume that the argument Value slice
// has the number and type of arguments given by typ.
// If typ describes a variadic function, the final Value is itself
// a slice representing the variadic arguments, as in the
// body of a variadic function. The result Value slice returned by fn
// must have the number and type of results given by typ.
// The Value.Call method allows the caller to invoke a typed function
// in terms of Values; in contrast, MakeFunc allows the caller to implement
// a typed function in terms of Values.
// The Examples section of the documentation includes an illustration
// of how to use MakeFunc to build a swap function for different types.
func MakeFunc(typ Type, fn func(args []Value) (results []Value)) Value {
if typ.Kind() != Func {
panic("reflect: call of MakeFunc with non-Func type")
t := typ.common()
ftyp := (*funcType)(unsafe.Pointer(t))
impl := &makeFuncImpl{
typ: ftyp,
fn: fn,
method: -1,
makeFuncFFI(ftyp, unsafe.Pointer(impl))
return Value{t, unsafe.Pointer(&impl), flag(Func) | flagIndir}
// makeMethodValue converts v from the rcvr+method index representation
// of a method value to an actual method func value, which is
// basically the receiver value with a special bit set, into a true
// func value - a value holding an actual func. The output is
// semantically equivalent to the input as far as the user of package
// reflect can tell, but the true func representation can be handled
// by code like Convert and Interface and Assign.
func makeMethodValue(op string, v Value) Value {
if v.flag&flagMethod == 0 {
panic("reflect: internal error: invalid use of makeMethodValue")
// Ignoring the flagMethod bit, v describes the receiver, not the method type.
fl := v.flag & (flagRO | flagAddr | flagIndir)
fl |= flag(v.typ.Kind())
rcvr := Value{v.typ, v.ptr, fl}
// v.Type returns the actual type of the method value.
ft := v.Type().(*rtype)
// Cause panic if method is not appropriate.
// The panic would still happen during the call if we omit this,
// but we want Interface() and other operations to fail early.
_, t, _ := methodReceiver(op, rcvr, int(v.flag)>>flagMethodShift)
ftyp := (*funcType)(unsafe.Pointer(t))
method := int(v.flag) >> flagMethodShift
fv := &makeFuncImpl{
typ: ftyp,
method: method,
rcvr: rcvr,
makeFuncFFI(ftyp, unsafe.Pointer(fv))
return Value{ft, unsafe.Pointer(&fv), v.flag&flagRO | flag(Func) | flagIndir}
// makeValueMethod takes a method function and returns a function that
// takes a value receiver and calls the real method with a pointer to
// it.
func makeValueMethod(v Value) Value {
typ := v.typ
if typ.Kind() != Func {
panic("reflect: call of makeValueMethod with non-Func type")
if v.flag&flagMethodFn == 0 {
panic("reflect: call of makeValueMethod with non-MethodFn")
t := typ.common()
ftyp := (*funcType)(unsafe.Pointer(t))
impl := &makeFuncImpl{
typ: ftyp,
method: -2,
rcvr: v,
makeFuncFFI(ftyp, unsafe.Pointer(impl))
return Value{t, unsafe.Pointer(&impl), v.flag&flagRO | flag(Func) | flagIndir}
// Call the function represented by a makeFuncImpl.
func (c *makeFuncImpl) call(in []Value) []Value {
if c.method == -1 {
return c.fn(in)
} else if c.method == -2 {
if c.typ.IsVariadic() {
return c.rcvr.CallSlice(in)
} else {
return c.rcvr.Call(in)
} else {
m := c.rcvr.Method(c.method)
if c.typ.IsVariadic() {
return m.CallSlice(in)
} else {
return m.Call(in)