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POC++ Callback -- How to decouple the call back type
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Id
6849287
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AcceptedAnswerId
6849456
AnswerCount
3
ClosedDate
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2
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CreationDate
2011-07-27T18:25:26.553
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2
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2011-07-29T18:50:27.390
LastEditDate
2011-07-27T19:20:24.793
LastEditorUserId
835887
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835887
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0
PostTypeId
1
Score
2
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4282
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text
Body
For example, in the following pseudo code, Class B need to call A::Action() through B::m_cb member. The objective is, how to make a general, non-template Callback class, so "B" does not have to be a template, and the "CallBack" can hold any kind of function signature. I ever use such code before, but now I can not find that implementation. All I remember is: - the "CallBack" itself is not a template, but it contains member template - the helper function template make_callback will instantiate CallBack object Can anyone give a poiinter? <pre><code>Class A { public: void Action(){//...}; }; class CallBack { //... // CallBack it self it is a NOT a template // It can wrap member template though }; class B { public: void SetCallback(CallBack to){ m_cb = to; } void do_something() { //... m_cb.Execute(); //... } private: CallBack m_cb; }; int main() { A obj1; CallBack cb = make_callback(&obj1, &A::Action); B obj2; obj2.SetCallback(cb); //.... obj2.do_something(); } </code></pre> Here is the sample code I got from this same website. I tried to improved it a little bit, so it can tolerate arbitrary call back function's return type. But it still can not handle arbitrary number of arguments, like in line 18. Also, , T is the pointer to member function, which should be depend on C. I don't know how to enforce this. <pre><code>#include <iostream> #include <memory> // INTERNAL CLASSES class CallbackSpecBase { public: virtual ~CallbackSpecBase() {} virtual void operator()(...) const = 0; }; template<class C, class T> class CallbackSpec : public CallbackSpecBase { public: CallbackSpec(C& o, T m) : obj(o), method(m) {} /*line 18*/ void operator()(...) const { (&obj->*method)(); } // how to pass "..." into method(...) private: C& obj; T method; }; // PUBLIC API class Callback { public: Callback() {} void operator()() { (*spec)(); } template<class C, class T> void set(C& o, T m) { spec.reset(new CallbackSpec<C, T>(o, m)); } private: std::auto_ptr<CallbackSpecBase> spec; }; // TEST CODE class Test { public: void foo() { std::cout << "Working" << std::endl; } void bar() { std::cout << "Like a charm" << std::endl; } }; int main() { Test t; Callback c; c.set(t, &Test::foo); c(); c.set(t, &Test::bar); c(); } </code></pre>
Tags
<c++><templates><types><callback><decouple>
Title
C++ Callback -- How to decouple the call back type
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1. PO
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1. USJohn Crane
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1. USJohn Crane
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 POC++ Callback -- How to decouple the call back type
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1. COTip: [Boost.Bind](http://www.boost.org/doc/libs/1_47_0/libs/bind/bind.html) already offers this kind of functionality so it spares you having to implement it yourself.
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 POC++ Callback -- How to decouple the call back type
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 USPaul Manta
2. COCan Boost.Bind handle arbitrary callback function signature? like arbitrary types, and arbitrary number of arguments?
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 POC++ Callback -- How to decouple the call back type
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 USJohn Crane

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