// makeThunk returns a thunk, a synthetic function that delegates to a
// concrete or interface method denoted by sel.Obj(). The resulting
// function has no receiver, but has an additional (first) regular
// parameter.
//
// Precondition: sel.Kind() == types.MethodExpr.
//
// type T int or: type T interface { meth() }
// func (t T) meth()
// f := T.meth
// var t T
// f(t) // calls t.meth()
//
// f is a synthetic wrapper defined as if by:
//
// f := func(t T) { return t.meth() }
//
// TODO(adonovan): opt: currently the stub is created even when used
// directly in a function call: C.f(i, 0). This is less efficient
// than inlining the stub.
//
// EXCLUSIVE_LOCKS_ACQUIRED(meth.Prog.methodsMu)
//
func makeThunk(prog *Program, sel *types.Selection) *Function {
if sel.Kind() != types.MethodExpr {
panic(sel)
}
// TODO(adonovan): opt: canonicalize the recv Type to avoid
// construct unnecessary duplicate thunks.
key := selectionKey{
kind: sel.Kind(),
recv: sel.Recv(),
obj: sel.Obj(),
index: fmt.Sprint(sel.Index()),
indirect: sel.Indirect(),
}
prog.methodsMu.Lock()
defer prog.methodsMu.Unlock()
fn, ok := prog.thunks[key]
if !ok {
fn = makeWrapper(prog, sel)
if fn.Signature.Recv() != nil {
panic(fn) // unexpected receiver
}
prog.thunks[key] = fn
}
return fn
}