166 lines
4.7 KiB
Go
166 lines
4.7 KiB
Go
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// Copyright 2012 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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// MakeFunc implementation.
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package reflect
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import (
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"internal/abi"
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"unsafe"
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)
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// makeFuncImpl is the closure value implementing the function
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// returned by MakeFunc.
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// The first three words are layed out like ffi_go_closure.
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type makeFuncImpl struct {
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code uintptr
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ffi_cif unsafe.Pointer
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ffi_fun func(unsafe.Pointer, unsafe.Pointer)
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typ *funcType
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fn func([]Value) []Value
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// For gccgo we use the same entry point for functions and for
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// method values.
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method int
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rcvr Value
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}
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// MakeFunc returns a new function of the given Type
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// that wraps the function fn. When called, that new function
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// does the following:
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//
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// - converts its arguments to a slice of Values.
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// - runs results := fn(args).
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// - returns the results as a slice of Values, one per formal result.
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//
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// The implementation fn can assume that the argument Value slice
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// has the number and type of arguments given by typ.
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// If typ describes a variadic function, the final Value is itself
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// a slice representing the variadic arguments, as in the
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// body of a variadic function. The result Value slice returned by fn
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// must have the number and type of results given by typ.
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//
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// The Value.Call method allows the caller to invoke a typed function
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// in terms of Values; in contrast, MakeFunc allows the caller to implement
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// a typed function in terms of Values.
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//
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// The Examples section of the documentation includes an illustration
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// of how to use MakeFunc to build a swap function for different types.
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//
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func MakeFunc(typ Type, fn func(args []Value) (results []Value)) Value {
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if typ.Kind() != Func {
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panic("reflect: call of MakeFunc with non-Func type")
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}
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t := typ.common()
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ftyp := (*funcType)(unsafe.Pointer(t))
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impl := &makeFuncImpl{
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typ: ftyp,
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fn: fn,
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method: -1,
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}
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makeFuncFFI(makeCIF(ftyp), unsafe.Pointer(impl))
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return Value{t, unsafe.Pointer(&impl), flag(Func) | flagIndir}
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}
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// makeMethodValue converts v from the rcvr+method index representation
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// of a method value to an actual method func value, which is
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// basically the receiver value with a special bit set, into a true
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// func value - a value holding an actual func. The output is
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// semantically equivalent to the input as far as the user of package
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// reflect can tell, but the true func representation can be handled
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// by code like Convert and Interface and Assign.
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func makeMethodValue(op string, v Value) Value {
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if v.flag&flagMethod == 0 {
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panic("reflect: internal error: invalid use of makeMethodValue")
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}
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// Ignoring the flagMethod bit, v describes the receiver, not the method type.
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fl := v.flag & (flagRO | flagAddr | flagIndir)
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fl |= flag(v.typ.Kind())
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rcvr := Value{v.typ, v.ptr, fl}
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// v.Type returns the actual type of the method value.
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ft := v.Type().(*rtype)
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// Cause panic if method is not appropriate.
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// The panic would still happen during the call if we omit this,
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// but we want Interface() and other operations to fail early.
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_, t, _ := methodReceiver(op, rcvr, int(v.flag)>>flagMethodShift)
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ftyp := (*funcType)(unsafe.Pointer(t))
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method := int(v.flag) >> flagMethodShift
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fv := &makeFuncImpl{
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typ: ftyp,
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method: method,
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rcvr: rcvr,
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}
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makeFuncFFI(makeCIF(ftyp), unsafe.Pointer(fv))
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return Value{ft, unsafe.Pointer(&fv), v.flag&flagRO | flag(Func) | flagIndir}
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}
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// makeValueMethod takes a method function and returns a function that
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// takes a value receiver and calls the real method with a pointer to
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// it.
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func makeValueMethod(v Value) Value {
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typ := v.typ
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if typ.Kind() != Func {
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panic("reflect: call of makeValueMethod with non-Func type")
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}
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if v.flag&flagMethodFn == 0 {
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panic("reflect: call of makeValueMethod with non-MethodFn")
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}
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t := typ.common()
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ftyp := (*funcType)(unsafe.Pointer(t))
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impl := &makeFuncImpl{
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typ: ftyp,
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method: -2,
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rcvr: v,
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}
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makeFuncFFI(makeCIF(ftyp), unsafe.Pointer(impl))
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return Value{t, unsafe.Pointer(&impl), v.flag&flagRO | flag(Func) | flagIndir}
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}
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// methodValueCallCodePtr and methodValueCall are only here to provide
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// something to return for the UnsafePointer method of a method value.
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func methodValueCallCodePtr() uintptr {
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return abi.FuncPCABI0(methodValueCall)
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}
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func methodValueCall() {
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panic("methodValueCall")
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}
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// Call the function represented by a makeFuncImpl.
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func (c *makeFuncImpl) call(in []Value) []Value {
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if c.method == -1 {
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return c.fn(in)
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} else if c.method == -2 {
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if c.typ.IsVariadic() {
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return c.rcvr.CallSlice(in)
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} else {
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return c.rcvr.Call(in)
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}
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} else {
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m := c.rcvr.Method(c.method)
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if c.typ.IsVariadic() {
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return m.CallSlice(in)
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} else {
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return m.Call(in)
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}
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}
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}
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