84 lines
2.5 KiB
C++
84 lines
2.5 KiB
C++
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#pragma once
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// Declared only so it can be partially specialized
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template <class Signature>
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class cFunctionRef;
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/** A light-weight, type-erased reference to a function object.
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### Usage
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`cFunctionRef` is used whenever you call a normal function with a lambda. e.g.
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one of the `cWorld::DoWith` functions,
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m_World->DoWithChunkAt(BlockPos, [](cChunk & a_Chunk) -> bool
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{
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...
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}
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);
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It looks like you're calling it with a lambda but that would require
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`DoWithChunkAt` to be a template. The function is really being called with
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`cFunctionRef<bool(cChunk&)>` which is constructed from the lambda via a
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templated constructor. This gives you a generic pointer to the lambda which
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doesn't depend on the type of the function object it references.
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### Notes
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- This is similar to a `std::function` but doesn't copy the function object.
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This means that mutable function objects will be modified for the caller but
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would not be if using a `std::function` (See #3990 for implications of this).
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- A `cFunctionRef` has no empty state but is non-owning and so is safe to call as
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long as the referred object is still alive. */
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template <class Ret, class... Args>
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class cFunctionRef<Ret(Args...)>
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{
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public:
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/** Construct from a function object. */
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template <class FunctionObject,
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typename std::enable_if< // Don't disable the default copy constructor
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!std::is_same<typename std::decay<FunctionObject>::type, cFunctionRef>::value,
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int>::type = 0
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>
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cFunctionRef(FunctionObject && a_FunctionObject)
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{
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// Store an opaque reference to the object.
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m_CallableData = &a_FunctionObject;
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// Along with a function that knows how to call the object.
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m_CallFunction = &ObjectFunctionCaller<FunctionObject>;
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}
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/** Call the referenced function object */
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Ret operator () (Args... a_Args)
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{
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return m_CallFunction(m_CallableData, std::forward<Args>(a_Args)...);
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}
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private:
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/** Function that performs the call. */
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template <class ObjectType>
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static Ret ObjectFunctionCaller(void * a_Callable, Args... a_Args)
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{
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// Convert opaque reference to the concrete type.
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using ObjectPtr = typename std::add_pointer<ObjectType>::type;
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auto & Object = *static_cast<ObjectPtr>(a_Callable);
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// Forward the call down to the object.
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return Object(std::forward<Args>(a_Args)...);
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}
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using cCallFunction = Ret(*)(void *, Args...);
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/** Type erased reference to a callable. */
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void * m_CallableData;
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/** Function that knows how to call the type erased reference. */
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cCallFunction m_CallFunction;
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};
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