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author | Frank Benoit <benoit@tionex.de> |
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date | Thu, 10 Apr 2008 11:20:26 +0200 |
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/*========================================================================== * weakref.d * Written in the D Programming Language (http://www.digitalmars.com/d) */ /*************************************************************************** * Creates a weak reference to a class instance. * * A weak reference lets you hold onto a pointer to an object without * preventing the garbage collector from collecting it. * If the garbage collector collects the object then the weak pointer will * become 'null'. Thus one should always check a weak pointer for null * before doing anything that depends upon it having a value. * * Tested with: * DMD 1.025 / Phobos 1.025 * DMD 1.025 / Tango 0.99.4 * * Usage example: --- class Something {} auto a = new Something(); auto wa = new WeakRef!(Something)(a); std.gc.fullCollect(); // Reference 'a' prevents collection so wa.ptr is non-null assert(wa.ptr is a); delete a; // 'a' is gone now, so wa.ptr magically becomes null assert(wa.ptr is null); --- * * * Author: William V. Baxter III * Contributors: * Date: 21 Jan 2008 * Copyright: (C) 2008 William Baxter * License: Public Domain where allowed by law, ZLIB/PNG otherwise. */ //=========================================================================== module dwt.dwthelper.WeakRef; private { alias void delegate(Object) DisposeEvt; extern (C) void rt_attachDisposeEvent( Object obj, DisposeEvt evt ); extern (C) void rt_detachDisposeEvent( Object obj, DisposeEvt evt ); } class WeakRef(T : Object) { private: size_t cast_ptr_; void unhook(Object o) { if (cast(size_t)cast(void*)o == cast_ptr_) { rt_detachDisposeEvent(o, &unhook); cast_ptr_ = 0; } } public: this(T tptr) { cast_ptr_ = cast(size_t)cast(void*)tptr; rt_attachDisposeEvent(tptr, &unhook); } ~this() { T p = ptr(); if (p) { rt_detachDisposeEvent(p, &unhook); } } T ptr() { return cast(T)cast(void*)cast_ptr_; } WeakRef dup() { return new WeakRef(ptr()); } int opEquals( Object o ){ if( auto other = cast( WeakRef!(T) )o ){ return other.cast_ptr_ is cast_ptr_; } return false; } hash_t toHash(){ return cast_ptr_; } }