mirror of
https://github.com/golang/go
synced 2024-11-19 00:04:40 -07:00
323 lines
8.8 KiB
Go
323 lines
8.8 KiB
Go
// Copyright 2013 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 ssa
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// This file defines utilities for method-set computation including
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// synthesis of wrapper methods.
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//
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// Wrappers include:
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// - indirection/promotion wrappers for methods of embedded fields.
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// - interface method wrappers for expressions I.f.
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// - bound method wrappers, for uncalled obj.Method closures.
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// TODO(adonovan): rename to wrappers.go.
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import (
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"fmt"
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"go/token"
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"code.google.com/p/go.tools/go/types"
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)
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// recvType returns the receiver type of method obj.
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func recvType(obj *types.Func) types.Type {
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return obj.Type().(*types.Signature).Recv().Type()
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}
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// Method returns the Function implementing method meth, building
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// wrapper methods on demand.
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//
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// Thread-safe.
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//
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// EXCLUSIVE_LOCKS_ACQUIRED(prog.methodsMu)
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//
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func (prog *Program) Method(meth *types.Selection) *Function {
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if meth == nil {
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panic("Method(nil)")
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}
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typ := meth.Recv()
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if prog.mode&LogSource != 0 {
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defer logStack("Method %s %v", typ, meth)()
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}
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prog.methodsMu.Lock()
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defer prog.methodsMu.Unlock()
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type methodSet map[string]*Function
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mset, _ := prog.methodSets.At(typ).(methodSet)
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if mset == nil {
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mset = make(methodSet)
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prog.methodSets.Set(typ, mset)
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}
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id := meth.Obj().Id()
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fn := mset[id]
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if fn == nil {
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fn = findMethod(prog, meth)
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mset[id] = fn
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}
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return fn
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}
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// declaredFunc returns the concrete function/method denoted by obj.
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// Panic ensues if there is none.
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//
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func (prog *Program) declaredFunc(obj *types.Func) *Function {
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if v := prog.packageLevelValue(obj); v != nil {
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return v.(*Function)
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}
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panic("no concrete method: " + obj.String())
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}
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// findMethod returns the concrete Function for the method meth,
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// synthesizing wrappers as needed.
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//
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// EXCLUSIVE_LOCKS_REQUIRED(prog.methodsMu)
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//
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func findMethod(prog *Program, meth *types.Selection) *Function {
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needsPromotion := len(meth.Index()) > 1
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obj := meth.Obj().(*types.Func)
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needsIndirection := !isPointer(recvType(obj)) && isPointer(meth.Recv())
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if needsPromotion || needsIndirection {
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return makeWrapper(prog, meth.Recv(), meth)
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}
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if _, ok := meth.Recv().Underlying().(*types.Interface); ok {
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return interfaceMethodWrapper(prog, meth.Recv(), obj)
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}
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return prog.declaredFunc(obj)
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}
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// makeWrapper returns a synthetic wrapper Function that optionally
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// performs receiver indirection, implicit field selections and then a
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// tailcall of a "promoted" method. For example, given these decls:
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//
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// type A struct {B}
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// type B struct {*C}
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// type C ...
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// func (*C) f()
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//
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// then makeWrapper(typ=A, obj={Func:(*C).f, Indices=[B,C,f]})
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// synthesize this wrapper method:
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//
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// func (a A) f() { return a.B.C->f() }
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//
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// prog is the program to which the synthesized method will belong.
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// typ is the receiver type of the wrapper method. obj is the
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// type-checker's object for the promoted method; its Func may be a
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// concrete or an interface method.
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//
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// EXCLUSIVE_LOCKS_REQUIRED(prog.methodsMu)
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//
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func makeWrapper(prog *Program, typ types.Type, meth *types.Selection) *Function {
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obj := meth.Obj().(*types.Func)
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oldsig := obj.Type().(*types.Signature)
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recv := types.NewVar(token.NoPos, nil, "recv", typ)
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description := fmt.Sprintf("wrapper for %s", obj)
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if prog.mode&LogSource != 0 {
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defer logStack("make %s to (%s)", description, typ)()
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}
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fn := &Function{
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name: obj.Name(),
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method: meth,
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Signature: changeRecv(oldsig, recv),
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Synthetic: description,
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Prog: prog,
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Pkg: prog.packages[obj.Pkg()],
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pos: obj.Pos(),
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}
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fn.startBody()
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fn.addSpilledParam(recv)
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createParams(fn)
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var v Value = fn.Locals[0] // spilled receiver
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if isPointer(typ) {
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// TODO(adonovan): consider emitting a nil-pointer check here
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// with a nice error message, like gc does.
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v = emitLoad(fn, v)
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}
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// Invariant: v is a pointer, either
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// value of *A receiver param, or
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// address of A spilled receiver.
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// We use pointer arithmetic (FieldAddr possibly followed by
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// Load) in preference to value extraction (Field possibly
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// preceded by Load).
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indices := meth.Index()
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v = emitImplicitSelections(fn, v, indices[:len(indices)-1])
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// Invariant: v is a pointer, either
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// value of implicit *C field, or
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// address of implicit C field.
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var c Call
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if _, ok := oldsig.Recv().Type().Underlying().(*types.Interface); !ok { // concrete method
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if !isPointer(oldsig.Recv().Type()) {
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v = emitLoad(fn, v)
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}
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c.Call.Value = prog.declaredFunc(obj)
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c.Call.Args = append(c.Call.Args, v)
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} else {
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c.Call.Method = obj
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c.Call.Value = emitLoad(fn, v)
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}
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for _, arg := range fn.Params[1:] {
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c.Call.Args = append(c.Call.Args, arg)
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}
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emitTailCall(fn, &c)
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fn.finishBody()
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return fn
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}
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// createParams creates parameters for wrapper method fn based on its
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// Signature.Params, which do not include the receiver.
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//
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func createParams(fn *Function) {
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var last *Parameter
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tparams := fn.Signature.Params()
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for i, n := 0, tparams.Len(); i < n; i++ {
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last = fn.addParamObj(tparams.At(i))
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}
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if fn.Signature.IsVariadic() {
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last.typ = types.NewSlice(last.typ)
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}
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}
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// Wrappers for standalone interface methods ----------------------------------
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// interfaceMethodWrapper returns a synthetic wrapper function
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// permitting an abstract method obj to be called like a standalone
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// function, e.g.:
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//
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// type I interface { f(x int) R }
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// m := I.f // wrapper
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// var i I
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// m(i, 0)
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//
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// The wrapper is defined as if by:
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//
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// func (i I) f(x int, ...) R {
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// return i.f(x, ...)
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// }
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//
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// typ is the type of the receiver (I here). It isn't necessarily
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// equal to the recvType(obj) because one interface may embed another.
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// TODO(adonovan): more tests.
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//
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// TODO(adonovan): opt: currently the stub is created even when used
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// in call position: I.f(i, 0). Clearly this is suboptimal.
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//
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// EXCLUSIVE_LOCKS_REQUIRED(prog.methodsMu)
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//
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func interfaceMethodWrapper(prog *Program, typ types.Type, obj *types.Func) *Function {
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// If one interface embeds another they'll share the same
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// wrappers for common methods. This is safe, but it might
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// confuse some tools because of the implicit interface
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// conversion applied to the first argument. If this becomes
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// a problem, we should include 'typ' in the memoization key.
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fn, ok := prog.ifaceMethodWrappers[obj]
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if !ok {
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description := "interface method wrapper"
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if prog.mode&LogSource != 0 {
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defer logStack("(%s).%s, %s", typ, obj.Name(), description)()
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}
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fn = &Function{
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name: obj.Name(),
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object: obj,
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Signature: obj.Type().(*types.Signature),
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Synthetic: description,
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pos: obj.Pos(),
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Prog: prog,
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Pkg: prog.packages[obj.Pkg()],
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}
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fn.startBody()
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fn.addParam("recv", typ, token.NoPos)
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createParams(fn)
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var c Call
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c.Call.Method = obj
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c.Call.Value = fn.Params[0]
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for _, arg := range fn.Params[1:] {
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c.Call.Args = append(c.Call.Args, arg)
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}
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emitTailCall(fn, &c)
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fn.finishBody()
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prog.ifaceMethodWrappers[obj] = fn
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}
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return fn
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}
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// Wrappers for bound methods -------------------------------------------------
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// boundMethodWrapper returns a synthetic wrapper function that
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// delegates to a concrete or interface method.
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// The wrapper has one free variable, the method's receiver.
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// Use MakeClosure with such a wrapper to construct a bound-method
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// closure. e.g.:
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//
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// type T int or: type T interface { meth() }
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// func (t T) meth()
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// var t T
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// f := t.meth
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// f() // calls t.meth()
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//
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// f is a closure of a synthetic wrapper defined as if by:
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//
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// f := func() { return t.meth() }
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//
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// EXCLUSIVE_LOCKS_ACQUIRED(meth.Prog.methodsMu)
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//
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func boundMethodWrapper(prog *Program, obj *types.Func) *Function {
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prog.methodsMu.Lock()
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defer prog.methodsMu.Unlock()
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fn, ok := prog.boundMethodWrappers[obj]
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if !ok {
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description := fmt.Sprintf("bound method wrapper for %s", obj)
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if prog.mode&LogSource != 0 {
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defer logStack("%s", description)()
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}
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fn = &Function{
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name: "bound$" + obj.FullName(),
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Signature: changeRecv(obj.Type().(*types.Signature), nil), // drop receiver
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Synthetic: description,
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Prog: prog,
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Pkg: prog.packages[obj.Pkg()],
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pos: obj.Pos(),
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}
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cap := &Capture{name: "recv", typ: recvType(obj), parent: fn}
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fn.FreeVars = []*Capture{cap}
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fn.startBody()
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createParams(fn)
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var c Call
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if _, ok := recvType(obj).Underlying().(*types.Interface); !ok { // concrete
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c.Call.Value = prog.declaredFunc(obj)
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c.Call.Args = []Value{cap}
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} else {
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c.Call.Value = cap
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c.Call.Method = obj
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}
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for _, arg := range fn.Params {
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c.Call.Args = append(c.Call.Args, arg)
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}
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emitTailCall(fn, &c)
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fn.finishBody()
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prog.boundMethodWrappers[obj] = fn
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}
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return fn
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}
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func changeRecv(s *types.Signature, recv *types.Var) *types.Signature {
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return types.NewSignature(nil, recv, s.Params(), s.Results(), s.IsVariadic())
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}
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