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342 lines
9.5 KiB
D
342 lines
9.5 KiB
D
// Written in the D programming language
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// This is part of the Phobos runtime libary for the D programming language.
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/********************************
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* Signals and Slots are an implementation of the Observer Pattern.
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* Essentially, when a Signal is emitted, a list of connected Observers
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* (called slots) are called.
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*
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* There have been several D implementations of Signals and Slots.
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* This version makes use of several new features in D, which make
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* using it simpler and less error prone. In particular, it is no
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* longer necessary to instrument the slots.
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*
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* References:
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* $(LINK2 http://scottcollins.net/articles/a-deeper-look-at-_signals-and-slots.html, A Deeper Look at Signals and Slots)$(BR)
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* $(LINK2 http://en.wikipedia.org/wiki/Observer_pattern, Observer pattern)$(BR)
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* $(LINK2 http://en.wikipedia.org/wiki/Signals_and_slots, Wikipedia)$(BR)
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* $(LINK2 http://boost.org/doc/html/$(SIGNALS).html, Boost Signals)$(BR)
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* $(LINK2 http://doc.trolltech.com/4.1/signalsandslots.html, Qt)$(BR)
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*
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* There has been a great deal of discussion in the D newsgroups
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* over this, and several implementations:
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*
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/announce/signal_slots_library_4825.html, signal slots library)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/Signals_and_Slots_in_D_42387.html, Signals and Slots in D)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/Dynamic_binding_--_Qt_s_Signals_and_Slots_vs_Objective-C_42260.html, Dynamic binding -- Qt's Signals and Slots vs Objective-C)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/Dissecting_the_SS_42377.html, Dissecting the SS)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/dwt/about_harmonia_454.html, about harmonia)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/announce/1502.html, Another event handling module)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/41825.html, Suggestion: signal/slot mechanism)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/13251.html, Signals and slots?)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/10714.html, Signals and slots ready for evaluation)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/digitalmars/D/1393.html, Signals & Slots for Walter)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/28456.html, Signal/Slot mechanism?)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/19470.html, Modern Features?)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/16592.html, Delegates vs interfaces)$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/16583.html, The importance of component programming (properties, signals and slots, etc))$(BR)
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* $(LINK2 http://www.digitalmars.com/d/archives/16368.html, signals and slots)$(BR)
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*
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* Bugs:
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* Slots can only be delegates formed from class objects or
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* interfaces to class objects. If a delegate to something else
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* is passed to connect(), such as a struct member function,
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* a nested function or a COM interface, undefined behavior
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* will result.
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*
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* Not safe for multiple threads operating on the same signals
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* or slots.
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* Macros:
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* WIKI = Phobos/StdSignals
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* SIGNALS=signals
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* Copyright:
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* Public Domain
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* Author: Walter Bright, Digital Mars, www.digitalmars.com
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*/
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module std.signals;
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import std.stdio;
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import std.c.stdlib : calloc, realloc, free;
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import std.outofmemory : _d_OutOfMemory;
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// Special function for internal use only.
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// Use of this is where the slot had better be a delegate
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// to an object or an interface that is part of an object.
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extern (C) Object _d_toObject(void* p);
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//debug=signal;
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/************************
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* Mixin to create a signal within a class object.
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*
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* Different signals can be added to a class by naming the mixins.
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*
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* Example:
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---
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import std.signals;
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import std.stdio;
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class Observer
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{ // our slot
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void watch(string msg, int i)
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{
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writefln("Observed msg '%s' and value %s", msg, i);
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}
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}
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class Foo
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{
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int value() { return _value; }
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int value(int v)
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{
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if (v != _value)
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{ _value = v;
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// call all the connected slots with the two parameters
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emit("setting new value", v);
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}
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return v;
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}
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// Mix in all the code we need to make Foo into a signal
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mixin Signal!(string, int);
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private :
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int _value;
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}
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void main()
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{
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Foo a = new Foo;
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Observer o = new Observer;
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a.value = 3; // should not call o.watch()
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a.connect(&o.watch); // o.watch is the slot
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a.value = 4; // should call o.watch()
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a.disconnect(&o.watch); // o.watch is no longer a slot
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a.value = 5; // so should not call o.watch()
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a.connect(&o.watch); // connect again
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a.value = 6; // should call o.watch()
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delete o; // destroying o should automatically disconnect it
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a.value = 7; // should not call o.watch()
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}
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---
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* which should print:
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* <pre>
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* Observed msg 'setting new value' and value 4
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* Observed msg 'setting new value' and value 6
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* </pre>
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*
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*/
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template Signal(T1...)
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{
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/***
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* A slot is implemented as a delegate.
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* The slot_t is the type of the delegate.
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* The delegate must be to an instance of a class or an interface
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* to a class instance.
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* Delegates to struct instances or nested functions must not be
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* used as slots.
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*/
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alias void delegate(T1) slot_t;
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/***
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* Call each of the connected slots, passing the argument(s) i to them.
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*/
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void emit( T1 i )
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{
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foreach (slot; slots[0 .. slots_idx])
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{ if (slot)
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slot(i);
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}
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}
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/***
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* Add a slot to the list of slots to be called when emit() is called.
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*/
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void connect(slot_t slot)
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{
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/* Do this:
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* slots ~= slot;
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* but use malloc() and friends instead
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*/
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auto len = slots.length;
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if (slots_idx == len)
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{
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if (slots.length == 0)
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{
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len = 4;
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auto p = std.signals.calloc(slot_t.sizeof, len);
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if (!p)
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std.signals._d_OutOfMemory();
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slots = (cast(slot_t*)p)[0 .. len];
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}
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else
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{
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len = len * 2 + 4;
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auto p = std.signals.realloc(slots.ptr, slot_t.sizeof * len);
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if (!p)
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std.signals._d_OutOfMemory();
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slots = (cast(slot_t*)p)[0 .. len];
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slots[slots_idx + 1 .. length] = null;
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}
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}
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slots[slots_idx++] = slot;
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L1:
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Object o = _d_toObject(slot.ptr);
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o.notifyRegister(&unhook);
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}
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/***
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* Remove a slot from the list of slots to be called when emit() is called.
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*/
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void disconnect( slot_t slot)
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{
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debug (signal) writefln("Signal.disconnect(slot)");
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for (size_t i = 0; i < slots_idx; )
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{
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if (slots[i] == slot)
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{ slots_idx--;
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slots[i] = slots[slots_idx];
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slots[slots_idx] = null; // not strictly necessary
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Object o = _d_toObject(slot.ptr);
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o.notifyUnRegister(&unhook);
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}
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else
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i++;
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}
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}
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/* **
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* Special function called when o is destroyed.
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* It causes any slots dependent on o to be removed from the list
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* of slots to be called by emit().
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*/
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void unhook(Object o)
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{
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debug (signal) writefln("Signal.unhook(o = %s)", cast(void*)o);
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for (size_t i = 0; i < slots_idx; )
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{
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if (_d_toObject(slots[i].ptr) is o)
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{ slots_idx--;
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slots[i] = slots[slots_idx];
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slots[slots_idx] = null; // not strictly necessary
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}
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else
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i++;
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}
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}
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/* **
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* There can be multiple destructors inserted by mixins.
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*/
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~this()
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{
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/* **
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* When this object is destroyed, need to let every slot
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* know that this object is destroyed so they are not left
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* with dangling references to it.
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*/
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if (slots)
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{
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foreach (slot; slots[0 .. slots_idx])
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{
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if (slot)
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{ Object o = _d_toObject(slot.ptr);
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o.notifyUnRegister(&unhook);
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}
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}
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std.signals.free(slots.ptr);
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slots = null;
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}
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}
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private:
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slot_t[] slots; // the slots to call from emit()
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size_t slots_idx; // used length of slots[]
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}
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// A function whose sole purpose is to get this module linked in
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// so the unittest will run.
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void linkin() { }
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unittest
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{
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class Observer
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{
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void watch(string msg, int i)
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{
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//writefln("Observed msg '%s' and value %s", msg, i);
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captured_value = i;
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captured_msg = msg;
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}
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void clear()
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{
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captured_value = 0;
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captured_msg = "";
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}
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public:
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int captured_value;
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string captured_msg;
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}
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class Foo
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{
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int value() { return _value; }
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int value(int v)
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{
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if (v != _value)
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{ _value = v;
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emit("setting new value", v);
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}
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return v;
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}
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mixin Signal!(string, int);
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private:
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int _value;
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}
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Foo a = new Foo;
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Observer o = new Observer;
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// check initial condition
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assert(o.captured_value == 0);
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assert(o.captured_msg == "");
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// set a value while no observation is in place
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a.value = 3;
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assert(o.captured_value == 0);
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assert(o.captured_msg == "");
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// connect the watcher and trigger it
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a.connect(&o.watch);
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a.value = 4;
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assert(o.captured_value == 4);
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assert(o.captured_msg == "setting new value");
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// disconnect the watcher and make sure it doesn't trigger
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a.disconnect(&o.watch);
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a.value = 5;
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assert(o.captured_value == 4);
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assert(o.captured_msg == "setting new value");
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// reconnect the watcher and make sure it triggers
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a.connect(&o.watch);
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a.value = 6;
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assert(o.captured_value == 6);
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assert(o.captured_msg == "setting new value");
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// delete the underlying object and make sure it doesn't cause
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// a crash or other problems
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delete o;
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a.value = 7;
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}
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