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comparison: xpcom/glue/nsISupportsUtils.h
xpcom/glue/nsISupportsUtils.h
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- TOR_BUG_9701
- changeset 15
- b8a032363ba2
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| -1:000000000000 | 0:fb8dd1a7041c |
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| 1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */ | |
| 2 /* This Source Code Form is subject to the terms of the Mozilla Public | |
| 3 * License, v. 2.0. If a copy of the MPL was not distributed with this | |
| 4 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ | |
| 5 | |
| 6 #ifndef nsISupportsUtils_h__ | |
| 7 #define nsISupportsUtils_h__ | |
| 8 | |
| 9 #include "nscore.h" | |
| 10 #include "nsISupportsBase.h" | |
| 11 #include "nsError.h" | |
| 12 #include "nsDebug.h" | |
| 13 #include "nsISupportsImpl.h" | |
| 14 #include "mozilla/TypeTraits.h" | |
| 15 | |
| 16 /** | |
| 17 * Macro for adding a reference to an interface. | |
| 18 * @param _ptr The interface pointer. | |
| 19 */ | |
| 20 #define NS_ADDREF(_ptr) \ | |
| 21 (_ptr)->AddRef() | |
| 22 | |
| 23 /** | |
| 24 * Macro for adding a reference to this. This macro should be used | |
| 25 * because NS_ADDREF (when tracing) may require an ambiguous cast | |
| 26 * from the pointers primary type to nsISupports. This macro sidesteps | |
| 27 * that entire problem. | |
| 28 */ | |
| 29 #define NS_ADDREF_THIS() \ | |
| 30 AddRef() | |
| 31 | |
| 32 | |
| 33 extern "C++" { | |
| 34 // ...because some one is accidentally including this file inside | |
| 35 // an |extern "C"| | |
| 36 | |
| 37 | |
| 38 // Making this a |inline| |template| allows |expr| to be evaluated only once, | |
| 39 // yet still denies you the ability to |AddRef()| an |nsCOMPtr|. | |
| 40 template <class T> | |
| 41 inline | |
| 42 void | |
| 43 ns_if_addref( T expr ) | |
| 44 { | |
| 45 if (expr) { | |
| 46 expr->AddRef(); | |
| 47 } | |
| 48 } | |
| 49 | |
| 50 } /* extern "C++" */ | |
| 51 | |
| 52 /** | |
| 53 * Macro for adding a reference to an interface that checks for nullptr. | |
| 54 * @param _expr The interface pointer. | |
| 55 */ | |
| 56 #define NS_IF_ADDREF(_expr) ns_if_addref(_expr) | |
| 57 | |
| 58 /* | |
| 59 * Given these declarations, it explicitly OK and efficient to end a `getter' with: | |
| 60 * | |
| 61 * NS_IF_ADDREF(*result = mThing); | |
| 62 * | |
| 63 * even if |mThing| is an |nsCOMPtr|. If |mThing| is an |nsCOMPtr|, however, it is still | |
| 64 * _illegal_ to say |NS_IF_ADDREF(mThing)|. | |
| 65 */ | |
| 66 | |
| 67 /** | |
| 68 * Macro for releasing a reference to an interface. | |
| 69 * @param _ptr The interface pointer. | |
| 70 */ | |
| 71 #define NS_RELEASE(_ptr) \ | |
| 72 do { \ | |
| 73 (_ptr)->Release(); \ | |
| 74 (_ptr) = 0; \ | |
| 75 } while (0) | |
| 76 | |
| 77 /** | |
| 78 * Macro for releasing a reference to this interface. | |
| 79 */ | |
| 80 #define NS_RELEASE_THIS() \ | |
| 81 Release() | |
| 82 | |
| 83 /** | |
| 84 * Macro for releasing a reference to an interface, except that this | |
| 85 * macro preserves the return value from the underlying Release call. | |
| 86 * The interface pointer argument will only be NULLed if the reference count | |
| 87 * goes to zero. | |
| 88 * | |
| 89 * @param _ptr The interface pointer. | |
| 90 * @param _rc The reference count. | |
| 91 */ | |
| 92 #define NS_RELEASE2(_ptr, _rc) \ | |
| 93 do { \ | |
| 94 _rc = (_ptr)->Release(); \ | |
| 95 if (0 == (_rc)) (_ptr) = 0; \ | |
| 96 } while (0) | |
| 97 | |
| 98 /** | |
| 99 * Macro for releasing a reference to an interface that checks for nullptr; | |
| 100 * @param _ptr The interface pointer. | |
| 101 */ | |
| 102 #define NS_IF_RELEASE(_ptr) \ | |
| 103 do { \ | |
| 104 if (_ptr) { \ | |
| 105 (_ptr)->Release(); \ | |
| 106 (_ptr) = 0; \ | |
| 107 } \ | |
| 108 } while (0) | |
| 109 | |
| 110 /* | |
| 111 * Often you have to cast an implementation pointer, e.g., |this|, to an | |
| 112 * |nsISupports*|, but because you have multiple inheritance, a simple cast | |
| 113 * is ambiguous. One could simply say, e.g., (given a base |nsIBase|), | |
| 114 * |static_cast<nsIBase*>(this)|; but that disguises the fact that what | |
| 115 * you are really doing is disambiguating the |nsISupports|. You could make | |
| 116 * that more obvious with a double cast, e.g., |static_cast<nsISupports*> | |
| 117 (* static_cast<nsIBase*>(this))|, but that is bulky and harder to read... | |
| 118 * | |
| 119 * The following macro is clean, short, and obvious. In the example above, | |
| 120 * you would use it like this: |NS_ISUPPORTS_CAST(nsIBase*, this)|. | |
| 121 */ | |
| 122 | |
| 123 #define NS_ISUPPORTS_CAST(__unambiguousBase, __expr) \ | |
| 124 static_cast<nsISupports*>(static_cast<__unambiguousBase>(__expr)) | |
| 125 | |
| 126 // a type-safe shortcut for calling the |QueryInterface()| member function | |
| 127 template <class T, class DestinationType> | |
| 128 inline | |
| 129 nsresult | |
| 130 CallQueryInterface( T* aSource, DestinationType** aDestination ) | |
| 131 { | |
| 132 // We permit nsISupports-to-nsISupports here so that one can still obtain | |
| 133 // the canonical nsISupports pointer with CallQueryInterface. | |
| 134 static_assert(!mozilla::IsSame<T, DestinationType>::value || | |
| 135 mozilla::IsSame<DestinationType, nsISupports>::value, | |
| 136 "don't use CallQueryInterface for compile-time-determinable casts"); | |
| 137 | |
| 138 NS_PRECONDITION(aSource, "null parameter"); | |
| 139 NS_PRECONDITION(aDestination, "null parameter"); | |
| 140 | |
| 141 return aSource->QueryInterface(NS_GET_TEMPLATE_IID(DestinationType), | |
| 142 reinterpret_cast<void**>(aDestination)); | |
| 143 } | |
| 144 | |
| 145 #endif /* __nsISupportsUtils_h */ |
