mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-10-31 14:15:30 +00:00
118 lines
4.3 KiB
C++
118 lines
4.3 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
|
|
* vim: set ts=8 sts=4 et sw=4 tw=99:
|
|
* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
#ifndef js_CallNonGenericMethod_h
|
|
#define js_CallNonGenericMethod_h
|
|
|
|
#include "jstypes.h"
|
|
|
|
#include "js/CallArgs.h"
|
|
|
|
namespace JS {
|
|
|
|
// Returns true if |v| is considered an acceptable this-value.
|
|
typedef bool (*IsAcceptableThis)(HandleValue v);
|
|
|
|
// Implements the guts of a method; guaranteed to be provided an acceptable
|
|
// this-value, as determined by a corresponding IsAcceptableThis method.
|
|
typedef bool (*NativeImpl)(JSContext *cx, CallArgs args);
|
|
|
|
namespace detail {
|
|
|
|
// DON'T CALL THIS DIRECTLY. It's for use only by CallNonGenericMethod!
|
|
extern JS_PUBLIC_API(bool)
|
|
CallMethodIfWrapped(JSContext *cx, IsAcceptableThis test, NativeImpl impl, CallArgs args);
|
|
|
|
} // namespace detail
|
|
|
|
// Methods usually act upon |this| objects only from a single global object and
|
|
// compartment. Sometimes, however, a method must act upon |this| values from
|
|
// multiple global objects or compartments. In such cases the |this| value a
|
|
// method might see will be wrapped, such that various access to the object --
|
|
// to its class, its private data, its reserved slots, and so on -- will not
|
|
// work properly without entering that object's compartment. This method
|
|
// implements a solution to this problem.
|
|
//
|
|
// To implement a method that accepts |this| values from multiple compartments,
|
|
// define two functions. The first function matches the IsAcceptableThis type
|
|
// and indicates whether the provided value is an acceptable |this| for the
|
|
// method; it must be a pure function only of its argument.
|
|
//
|
|
// static const JSClass AnswerClass = { ... };
|
|
//
|
|
// static bool
|
|
// IsAnswerObject(const Value &v)
|
|
// {
|
|
// if (!v.isObject())
|
|
// return false;
|
|
// return JS_GetClass(&v.toObject()) == &AnswerClass;
|
|
// }
|
|
//
|
|
// The second function implements the NativeImpl signature and defines the
|
|
// behavior of the method when it is provided an acceptable |this| value.
|
|
// Aside from some typing niceties -- see the CallArgs interface for details --
|
|
// its interface is the same as that of JSNative.
|
|
//
|
|
// static bool
|
|
// answer_getAnswer_impl(JSContext *cx, JS::CallArgs args)
|
|
// {
|
|
// args.rval().setInt32(42);
|
|
// return true;
|
|
// }
|
|
//
|
|
// The implementation function is guaranteed to be called *only* with a |this|
|
|
// value which is considered acceptable.
|
|
//
|
|
// Now to implement the actual method, write a JSNative that calls the method
|
|
// declared below, passing the appropriate template and runtime arguments.
|
|
//
|
|
// static bool
|
|
// answer_getAnswer(JSContext *cx, unsigned argc, JS::Value *vp)
|
|
// {
|
|
// JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
|
|
// return JS::CallNonGenericMethod<IsAnswerObject, answer_getAnswer_impl>(cx, args);
|
|
// }
|
|
//
|
|
// Note that, because they are used as template arguments, the predicate
|
|
// and implementation functions must have external linkage. (This is
|
|
// unfortunate, but GCC wasn't inlining things as one would hope when we
|
|
// passed them as function arguments.)
|
|
//
|
|
// JS::CallNonGenericMethod will test whether |args.thisv()| is acceptable. If
|
|
// it is, it will call the provided implementation function, which will return
|
|
// a value and indicate success. If it is not, it will attempt to unwrap
|
|
// |this| and call the implementation function on the unwrapped |this|. If
|
|
// that succeeds, all well and good. If it doesn't succeed, a TypeError will
|
|
// be thrown.
|
|
//
|
|
// Note: JS::CallNonGenericMethod will only work correctly if it's called in
|
|
// tail position in a JSNative. Do not call it from any other place.
|
|
//
|
|
template<IsAcceptableThis Test, NativeImpl Impl>
|
|
MOZ_ALWAYS_INLINE bool
|
|
CallNonGenericMethod(JSContext *cx, CallArgs args)
|
|
{
|
|
HandleValue thisv = args.thisv();
|
|
if (Test(thisv))
|
|
return Impl(cx, args);
|
|
|
|
return detail::CallMethodIfWrapped(cx, Test, Impl, args);
|
|
}
|
|
|
|
MOZ_ALWAYS_INLINE bool
|
|
CallNonGenericMethod(JSContext *cx, IsAcceptableThis Test, NativeImpl Impl, CallArgs args)
|
|
{
|
|
HandleValue thisv = args.thisv();
|
|
if (Test(thisv))
|
|
return Impl(cx, args);
|
|
|
|
return detail::CallMethodIfWrapped(cx, Test, Impl, args);
|
|
}
|
|
|
|
} // namespace JS
|
|
|
|
#endif /* js_CallNonGenericMethod_h */
|