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85 lines
2.5 KiB
Markdown
85 lines
2.5 KiB
Markdown
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# Heterogeneous classes
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## Description
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'CallbackList', 'EventDispatcher', and 'EventQueue' are homogeneous. All listeners must have the same prototype. For example,
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```c++
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eventpp::EventDispatcher<int, void ()> dispatcher;
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dispatcher.appendListener(3, []() {}); // OK
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dispatcher.appendListener(3, [](std::string) {}); // wrong, can't listen for void(std::string)
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```
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There are heterogeneous counterparts, 'HeterCallbackList', 'HeterEventDispatcher', and 'HeterEventQueue'. These classes allow listeners having different prototypes. For example,
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```c++
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eventpp::HeterEventDispatcher<int, eventpp::HeterTuple<void (), void (std::string)> > dispatcher;
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dispatcher.appendListener(3, []() {}); // OK
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dispatcher.appendListener(3, [](std::string) {}); // OK
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```
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## Usage
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### Headers
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eventpp/hetercallbacklist.h
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eventpp/hetereventdispatcher.h
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eventpp/hetereventqueue.h
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### Template parameters
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```c++
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template <
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typename PrototypeList,
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typename Policies = DefaultPolicies
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>
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class HeterCallbackList;
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template <
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typename Event,
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typename PrototypeList,
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typename Policies = DefaultPolicies
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>
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class HeterEventDispatcher;
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template <
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typename Event,
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typename PrototypeList,
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typename Policies = DefaultPolicies
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>
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class HeterEventQueue;
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```
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For comparison, below are the template parameters for the homogeneous counterparts
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```c++
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template <
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typename Prototype,
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typename Policies = DefaultPolicies
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>
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class CallbackList;
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template <
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typename Event,
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typename Prototype,
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typename Policies = DefaultPolicies
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>
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class EventDispatcher;
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template <
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typename Event,
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typename Prototype,
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typename Policies = DefaultPolicies
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>
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class EventQueue;
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```
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The only difference is the `Prototype` in homo-classes becomes `PrototypeList` in heter-classes.
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In the homo-classes, `Prototype` is a single function type such as `void ()`.
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In the heter-classes, `PrototypeList` is a list of function types in `eventpp::HeterTuple`, such as `eventpp::HeterTuple<void (), void (std::string), void (int, int)>`.
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Note: Ideally it would be better to use `std::tuple` instead of `eventpp::HeterTuple`, but the problem is that the tuple is instantiated in HeterEventDispatcher which cause compile error that function type can't be instantiated.
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### Member functions and types
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The heter-classes have similar functions and types as the homo-classes. The major difference is, in the homo-classes, listeners can have only one prototype, while in the heter-classes, listeners can have any prototypes which are in the `PrototypeList` specified in the class template parameters.
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