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comparison: js/public/CallNonGenericMethod.h
js/public/CallNonGenericMethod.h
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| -1:000000000000 | 0:51a30e4557d8 |
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| 1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- | |
| 2 * vim: set ts=8 sts=4 et sw=4 tw=99: | |
| 3 * This Source Code Form is subject to the terms of the Mozilla Public | |
| 4 * License, v. 2.0. If a copy of the MPL was not distributed with this | |
| 5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ | |
| 6 | |
| 7 #ifndef js_CallNonGenericMethod_h | |
| 8 #define js_CallNonGenericMethod_h | |
| 9 | |
| 10 #include "jstypes.h" | |
| 11 | |
| 12 #include "js/CallArgs.h" | |
| 13 | |
| 14 namespace JS { | |
| 15 | |
| 16 // Returns true if |v| is considered an acceptable this-value. | |
| 17 typedef bool (*IsAcceptableThis)(HandleValue v); | |
| 18 | |
| 19 // Implements the guts of a method; guaranteed to be provided an acceptable | |
| 20 // this-value, as determined by a corresponding IsAcceptableThis method. | |
| 21 typedef bool (*NativeImpl)(JSContext *cx, CallArgs args); | |
| 22 | |
| 23 namespace detail { | |
| 24 | |
| 25 // DON'T CALL THIS DIRECTLY. It's for use only by CallNonGenericMethod! | |
| 26 extern JS_PUBLIC_API(bool) | |
| 27 CallMethodIfWrapped(JSContext *cx, IsAcceptableThis test, NativeImpl impl, CallArgs args); | |
| 28 | |
| 29 } // namespace detail | |
| 30 | |
| 31 // Methods usually act upon |this| objects only from a single global object and | |
| 32 // compartment. Sometimes, however, a method must act upon |this| values from | |
| 33 // multiple global objects or compartments. In such cases the |this| value a | |
| 34 // method might see will be wrapped, such that various access to the object -- | |
| 35 // to its class, its private data, its reserved slots, and so on -- will not | |
| 36 // work properly without entering that object's compartment. This method | |
| 37 // implements a solution to this problem. | |
| 38 // | |
| 39 // To implement a method that accepts |this| values from multiple compartments, | |
| 40 // define two functions. The first function matches the IsAcceptableThis type | |
| 41 // and indicates whether the provided value is an acceptable |this| for the | |
| 42 // method; it must be a pure function only of its argument. | |
| 43 // | |
| 44 // static const JSClass AnswerClass = { ... }; | |
| 45 // | |
| 46 // static bool | |
| 47 // IsAnswerObject(const Value &v) | |
| 48 // { | |
| 49 // if (!v.isObject()) | |
| 50 // return false; | |
| 51 // return JS_GetClass(&v.toObject()) == &AnswerClass; | |
| 52 // } | |
| 53 // | |
| 54 // The second function implements the NativeImpl signature and defines the | |
| 55 // behavior of the method when it is provided an acceptable |this| value. | |
| 56 // Aside from some typing niceties -- see the CallArgs interface for details -- | |
| 57 // its interface is the same as that of JSNative. | |
| 58 // | |
| 59 // static bool | |
| 60 // answer_getAnswer_impl(JSContext *cx, JS::CallArgs args) | |
| 61 // { | |
| 62 // args.rval().setInt32(42); | |
| 63 // return true; | |
| 64 // } | |
| 65 // | |
| 66 // The implementation function is guaranteed to be called *only* with a |this| | |
| 67 // value which is considered acceptable. | |
| 68 // | |
| 69 // Now to implement the actual method, write a JSNative that calls the method | |
| 70 // declared below, passing the appropriate template and runtime arguments. | |
| 71 // | |
| 72 // static bool | |
| 73 // answer_getAnswer(JSContext *cx, unsigned argc, JS::Value *vp) | |
| 74 // { | |
| 75 // JS::CallArgs args = JS::CallArgsFromVp(argc, vp); | |
| 76 // return JS::CallNonGenericMethod<IsAnswerObject, answer_getAnswer_impl>(cx, args); | |
| 77 // } | |
| 78 // | |
| 79 // Note that, because they are used as template arguments, the predicate | |
| 80 // and implementation functions must have external linkage. (This is | |
| 81 // unfortunate, but GCC wasn't inlining things as one would hope when we | |
| 82 // passed them as function arguments.) | |
| 83 // | |
| 84 // JS::CallNonGenericMethod will test whether |args.thisv()| is acceptable. If | |
| 85 // it is, it will call the provided implementation function, which will return | |
| 86 // a value and indicate success. If it is not, it will attempt to unwrap | |
| 87 // |this| and call the implementation function on the unwrapped |this|. If | |
| 88 // that succeeds, all well and good. If it doesn't succeed, a TypeError will | |
| 89 // be thrown. | |
| 90 // | |
| 91 // Note: JS::CallNonGenericMethod will only work correctly if it's called in | |
| 92 // tail position in a JSNative. Do not call it from any other place. | |
| 93 // | |
| 94 template<IsAcceptableThis Test, NativeImpl Impl> | |
| 95 MOZ_ALWAYS_INLINE bool | |
| 96 CallNonGenericMethod(JSContext *cx, CallArgs args) | |
| 97 { | |
| 98 HandleValue thisv = args.thisv(); | |
| 99 if (Test(thisv)) | |
| 100 return Impl(cx, args); | |
| 101 | |
| 102 return detail::CallMethodIfWrapped(cx, Test, Impl, args); | |
| 103 } | |
| 104 | |
| 105 MOZ_ALWAYS_INLINE bool | |
| 106 CallNonGenericMethod(JSContext *cx, IsAcceptableThis Test, NativeImpl Impl, CallArgs args) | |
| 107 { | |
| 108 HandleValue thisv = args.thisv(); | |
| 109 if (Test(thisv)) | |
| 110 return Impl(cx, args); | |
| 111 | |
| 112 return detail::CallMethodIfWrapped(cx, Test, Impl, args); | |
| 113 } | |
| 114 | |
| 115 } // namespace JS | |
| 116 | |
| 117 #endif /* js_CallNonGenericMethod_h */ |
