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1 /*==========================================================================
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2 * weakref.d
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3 * Written in the D Programming Language (http://www.digitalmars.com/d)
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4 */
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5 /***************************************************************************
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6 * Creates a weak reference to a class instance.
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7 *
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8 * A weak reference lets you hold onto a pointer to an object without
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9 * preventing the garbage collector from collecting it.
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10 * If the garbage collector collects the object then the weak pointer will
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11 * become 'null'. Thus one should always check a weak pointer for null
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12 * before doing anything that depends upon it having a value.
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13 *
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14 * Tested with:
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15 * DMD 1.025 / Phobos 1.025
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16 * DMD 1.025 / Tango 0.99.4
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17 *
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18 * Usage example:
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19 ---
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20 class Something {}
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21
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22 auto a = new Something();
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23 auto wa = new WeakRef!(Something)(a);
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24 std.gc.fullCollect();
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25
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26 // Reference 'a' prevents collection so wa.ptr is non-null
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27 assert(wa.ptr is a);
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28
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29 delete a;
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30
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31 // 'a' is gone now, so wa.ptr magically becomes null
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32 assert(wa.ptr is null);
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33 ---
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34 *
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35 *
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36 * Author: William V. Baxter III
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37 * Contributors:
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38 * Date: 21 Jan 2008
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39 * Copyright: (C) 2008 William Baxter
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40 * License: Public Domain where allowed by law, ZLIB/PNG otherwise.
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41 */
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42 //===========================================================================
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43
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44 module dwt.dwthelper.WeakRef;
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45
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46 private {
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47 alias void delegate(Object) DisposeEvt;
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48 extern (C) void rt_attachDisposeEvent( Object obj, DisposeEvt evt );
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49 extern (C) void rt_detachDisposeEvent( Object obj, DisposeEvt evt );
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50 }
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51
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52 class WeakRef(T : Object) {
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53 private:
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54 size_t cast_ptr_;
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55 void unhook(Object o) {
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56 if (cast(size_t)cast(void*)o == cast_ptr_) {
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57 rt_detachDisposeEvent(o, &unhook);
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58 cast_ptr_ = 0;
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59 }
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60 }
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61 public:
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62
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63 this(T tptr) {
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64 cast_ptr_ = cast(size_t)cast(void*)tptr;
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65 rt_attachDisposeEvent(tptr, &unhook);
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66 }
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67 ~this() {
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68 T p = ptr();
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69 if (p) {
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70 rt_detachDisposeEvent(p, &unhook);
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71 }
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72 }
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73 T ptr() {
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74 return cast(T)cast(void*)cast_ptr_;
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75 }
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76 WeakRef dup() {
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77 return new WeakRef(ptr());
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78 }
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79 int opEquals( Object o ){
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80 if( auto other = cast( WeakRef!(T) )o ){
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81 return other.cast_ptr_ is cast_ptr_;
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82 }
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83 return false;
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84 }
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85 hash_t toHash(){
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86 return cast_ptr_;
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87 }
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88 }
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