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56 lines
2.1 KiB
C
56 lines
2.1 KiB
C
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: set ts=8 sts=4 et sw=4 tw=99:
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef js_IdForward_h
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#define js_IdForward_h
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#include <stddef.h>
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// A jsid is an identifier for a property or method of an object which is
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// either a 31-bit signed integer, interned string or object.
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//
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// Also, there is an additional jsid value, JSID_VOID, which does not occur in
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// JS scripts but may be used to indicate the absence of a valid jsid. A void
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// jsid is not a valid id and only arises as an exceptional API return value,
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// such as in JS_NextProperty. Embeddings must not pass JSID_VOID into JSAPI
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// entry points expecting a jsid and do not need to handle JSID_VOID in hooks
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// receiving a jsid except when explicitly noted in the API contract.
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//
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// A jsid is not implicitly convertible to or from a jsval; JS_ValueToId or
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// JS_IdToValue must be used instead.
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//
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// In release builds, jsid is defined to be an integral type. This
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// prevents many bugs from being caught at compile time. E.g.:
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//
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// jsid id = ...
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// if (id) // error
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// ...
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//
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// size_t n = id; // error
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//
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// To catch more errors, jsid is given a struct type in C++ debug builds.
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// Struct assignment and (in C++) operator== allow correct code to be mostly
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// oblivious to the change. This feature can be explicitly disabled in debug
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// builds by defining JS_NO_JSVAL_JSID_STRUCT_TYPES.
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//
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// Note: if jsid was always a struct, we could just forward declare it in
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// places where its declaration is needed. But the fact that it's a typedef in
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// non-debug builds prevents that. So we have this file, which is morally
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// equivalent to a forward declaration, and should be included by any file that
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// uses jsid but doesn't need its definition.
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#if defined(DEBUG) && !defined(JS_NO_JSVAL_JSID_STRUCT_TYPES)
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# define JS_USE_JSID_STRUCT_TYPES
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#endif
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#ifdef JS_USE_JSID_STRUCT_TYPES
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struct jsid;
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#else
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typedef ptrdiff_t jsid;
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#endif
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#endif /* js_IdForward_h */
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