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/*
* Copyright 2015 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkFunction_DEFINED
#define SkFunction_DEFINED
// TODO: document
#include "SkTypes.h"
#include "SkTLogic.h"
template <typename> class SkFunction;
template <typename R, typename... Args>
class SkFunction<R(Args...)> : SkNoncopyable {
public:
explicit SkFunction(R (*fn)(Args...)) : fVTable(GetFunctionPointerVTable()) {
// We've been passed a function pointer. We'll just store it.
fFunction = reinterpret_cast<void*>(fn);
}
template <typename Fn>
explicit SkFunction(Fn fn, SK_WHEN_C((sizeof(Fn) > sizeof(void*)), void*) = nullptr)
: fVTable(GetOutlineVTable<Fn>()) {
// We've got a functor larger than a pointer. We've go to copy it onto the heap.
fFunction = SkNEW_ARGS(Fn, (fn));
}
template <typename Fn>
explicit SkFunction(Fn fn, SK_WHEN_C((sizeof(Fn) <= sizeof(void*)), void*) = nullptr)
: fVTable(GetInlineVTable<Fn>()) {
// We've got a functor that fits in a pointer. We copy it right inline.
SkNEW_PLACEMENT_ARGS(&fFunction, Fn, (fn));
}
~SkFunction() { fVTable.fCleanUp(fFunction); }
R operator()(Args... args) { return fVTable.fCall(fFunction, args...); }
private:
struct VTable {
R (*fCall)(void*, Args...);
void (*fCleanUp)(void*);
};
// Used when fFunction is a function pointer of type R(*)(Args...).
static const VTable& GetFunctionPointerVTable() {
static const VTable vtable = {
[](void* fn, Args... args) { return reinterpret_cast<R(*)(Args...)>(fn)(args...); },
[](void*) { /* Nothing to clean up for function pointers. */ }
};
return vtable;
}
// Used when fFunction is a pointer to a functor of type Fn on the heap (we own it).
template <typename Fn>
static const VTable& GetOutlineVTable() {
static const VTable vtable = {
[](void* fn, Args... args) { return (*static_cast<Fn*>(fn))(args...); },
[](void* fn) { SkDELETE(static_cast<Fn*>(fn)); },
};
return vtable;
}
// Used when fFunction _is_ a functor of type Fn, not a pointer to the functor.
template <typename Fn>
static const VTable& GetInlineVTable() {
static const VTable vtable = {
[](void* fn, Args... args) {
union { void* p; Fn f; } pun = { fn };
return pun.f(args...);
},
[](void* fn) {
union { void* p; Fn f; } pun = { fn };
pun.f.~Fn();
(void)(pun.f); // Otherwise, when ~Fn() is trivial, MSVC complains pun is unused.
}
};
return vtable;
}
void* fFunction; // A function pointer, a pointer to a functor, or an inlined functor.
const VTable& fVTable; // How to call, delete (and one day copy, move) fFunction.
};
// TODO:
// - is it worth moving fCall out of the VTable into SkFunction itself to avoid the indirection?
// - should constructors be implicit?
// - make SkFunction copyable
// - emulate std::forward for moveable functors (e.g. lambdas)
// - forward args too?
#endif//SkFunction_DEFINED
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