cannam@49: // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
cannam@49: // Licensed under the MIT License:
cannam@49: //
cannam@49: // Permission is hereby granted, free of charge, to any person obtaining a copy
cannam@49: // of this software and associated documentation files (the "Software"), to deal
cannam@49: // in the Software without restriction, including without limitation the rights
cannam@49: // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
cannam@49: // copies of the Software, and to permit persons to whom the Software is
cannam@49: // furnished to do so, subject to the following conditions:
cannam@49: //
cannam@49: // The above copyright notice and this permission notice shall be included in
cannam@49: // all copies or substantial portions of the Software.
cannam@49: //
cannam@49: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
cannam@49: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
cannam@49: // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
cannam@49: // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
cannam@49: // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
cannam@49: // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
cannam@49: // THE SOFTWARE.
cannam@49: 
cannam@49: #ifndef KJ_FUNCTION_H_
cannam@49: #define KJ_FUNCTION_H_
cannam@49: 
cannam@49: #if defined(__GNUC__) && !KJ_HEADER_WARNINGS
cannam@49: #pragma GCC system_header
cannam@49: #endif
cannam@49: 
cannam@49: #include "memory.h"
cannam@49: 
cannam@49: namespace kj {
cannam@49: 
cannam@49: template <typename Signature>
cannam@49: class Function;
cannam@49: // Function wrapper using virtual-based polymorphism.  Use this when template polymorphism is
cannam@49: // not possible.  You can, for example, accept a Function as a parameter:
cannam@49: //
cannam@49: //     void setFilter(Function<bool(const Widget&)> filter);
cannam@49: //
cannam@49: // The caller of `setFilter()` may then pass any callable object as the parameter.  The callable
cannam@49: // object does not have to have the exact signature specified, just one that is "compatible" --
cannam@49: // i.e. the return type is covariant and the parameters are contravariant.
cannam@49: //
cannam@49: // Unlike `std::function`, `kj::Function`s are movable but not copyable, just like `kj::Own`.  This
cannam@49: // is to avoid unexpected heap allocation or slow atomic reference counting.
cannam@49: //
cannam@49: // When a `Function` is constructed from an lvalue, it captures only a reference to the value.
cannam@49: // When constructed from an rvalue, it invokes the value's move constructor.  So, for example:
cannam@49: //
cannam@49: //     struct AddN {
cannam@49: //       int n;
cannam@49: //       int operator(int i) { return i + n; }
cannam@49: //     }
cannam@49: //
cannam@49: //     Function<int(int, int)> f1 = AddN{2};
cannam@49: //     // f1 owns an instance of AddN.  It may safely be moved out
cannam@49: //     // of the local scope.
cannam@49: //
cannam@49: //     AddN adder(2);
cannam@49: //     Function<int(int, int)> f2 = adder;
cannam@49: //     // f2 contains a reference to `adder`.  Thus, it becomes invalid
cannam@49: //     // when `adder` goes out-of-scope.
cannam@49: //
cannam@49: //     AddN adder2(2);
cannam@49: //     Function<int(int, int)> f3 = kj::mv(adder2);
cannam@49: //     // f3 owns an insatnce of AddN moved from `adder2`.  f3 may safely
cannam@49: //     // be moved out of the local scope.
cannam@49: //
cannam@49: // Additionally, a Function may be bound to a class method using KJ_BIND_METHOD(object, methodName).
cannam@49: // For example:
cannam@49: //
cannam@49: //     class Printer {
cannam@49: //     public:
cannam@49: //       void print(int i);
cannam@49: //       void print(kj::StringPtr s);
cannam@49: //     };
cannam@49: //
cannam@49: //     Printer p;
cannam@49: //
cannam@49: //     Function<void(uint)> intPrinter = KJ_BIND_METHOD(p, print);
cannam@49: //     // Will call Printer::print(int).
cannam@49: //
cannam@49: //     Function<void(const char*)> strPrinter = KJ_BIND_METHOD(p, print);
cannam@49: //     // Will call Printer::print(kj::StringPtr).
cannam@49: //
cannam@49: // Notice how KJ_BIND_METHOD is able to figure out which overload to use depending on the kind of
cannam@49: // Function it is binding to.
cannam@49: 
cannam@49: template <typename Signature>
cannam@49: class ConstFunction;
cannam@49: // Like Function, but wraps a "const" (i.e. thread-safe) call.
cannam@49: 
cannam@49: template <typename Return, typename... Params>
cannam@49: class Function<Return(Params...)> {
cannam@49: public:
cannam@49:   template <typename F>
cannam@49:   inline Function(F&& f): impl(heap<Impl<F>>(kj::fwd<F>(f))) {}
cannam@49:   Function() = default;
cannam@49: 
cannam@49:   // Make sure people don't accidentally end up wrapping a reference when they meant to return
cannam@49:   // a function.
cannam@49:   KJ_DISALLOW_COPY(Function);
cannam@49:   Function(Function&) = delete;
cannam@49:   Function& operator=(Function&) = delete;
cannam@49:   template <typename T> Function(const Function<T>&) = delete;
cannam@49:   template <typename T> Function& operator=(const Function<T>&) = delete;
cannam@49:   template <typename T> Function(const ConstFunction<T>&) = delete;
cannam@49:   template <typename T> Function& operator=(const ConstFunction<T>&) = delete;
cannam@49:   Function(Function&&) = default;
cannam@49:   Function& operator=(Function&&) = default;
cannam@49: 
cannam@49:   inline Return operator()(Params... params) {
cannam@49:     return (*impl)(kj::fwd<Params>(params)...);
cannam@49:   }
cannam@49: 
cannam@49:   Function reference() {
cannam@49:     // Forms a new Function of the same type that delegates to this Function by reference.
cannam@49:     // Therefore, this Function must outlive the returned Function, but otherwise they behave
cannam@49:     // exactly the same.
cannam@49: 
cannam@49:     return *impl;
cannam@49:   }
cannam@49: 
cannam@49: private:
cannam@49:   class Iface {
cannam@49:   public:
cannam@49:     virtual Return operator()(Params... params) = 0;
cannam@49:   };
cannam@49: 
cannam@49:   template <typename F>
cannam@49:   class Impl final: public Iface {
cannam@49:   public:
cannam@49:     explicit Impl(F&& f): f(kj::fwd<F>(f)) {}
cannam@49: 
cannam@49:     Return operator()(Params... params) override {
cannam@49:       return f(kj::fwd<Params>(params)...);
cannam@49:     }
cannam@49: 
cannam@49:   private:
cannam@49:     F f;
cannam@49:   };
cannam@49: 
cannam@49:   Own<Iface> impl;
cannam@49: };
cannam@49: 
cannam@49: template <typename Return, typename... Params>
cannam@49: class ConstFunction<Return(Params...)> {
cannam@49: public:
cannam@49:   template <typename F>
cannam@49:   inline ConstFunction(F&& f): impl(heap<Impl<F>>(kj::fwd<F>(f))) {}
cannam@49:   ConstFunction() = default;
cannam@49: 
cannam@49:   // Make sure people don't accidentally end up wrapping a reference when they meant to return
cannam@49:   // a function.
cannam@49:   KJ_DISALLOW_COPY(ConstFunction);
cannam@49:   ConstFunction(ConstFunction&) = delete;
cannam@49:   ConstFunction& operator=(ConstFunction&) = delete;
cannam@49:   template <typename T> ConstFunction(const ConstFunction<T>&) = delete;
cannam@49:   template <typename T> ConstFunction& operator=(const ConstFunction<T>&) = delete;
cannam@49:   template <typename T> ConstFunction(const Function<T>&) = delete;
cannam@49:   template <typename T> ConstFunction& operator=(const Function<T>&) = delete;
cannam@49:   ConstFunction(ConstFunction&&) = default;
cannam@49:   ConstFunction& operator=(ConstFunction&&) = default;
cannam@49: 
cannam@49:   inline Return operator()(Params... params) const {
cannam@49:     return (*impl)(kj::fwd<Params>(params)...);
cannam@49:   }
cannam@49: 
cannam@49:   ConstFunction reference() const {
cannam@49:     // Forms a new ConstFunction of the same type that delegates to this ConstFunction by reference.
cannam@49:     // Therefore, this ConstFunction must outlive the returned ConstFunction, but otherwise they
cannam@49:     // behave exactly the same.
cannam@49: 
cannam@49:     return *impl;
cannam@49:   }
cannam@49: 
cannam@49: private:
cannam@49:   class Iface {
cannam@49:   public:
cannam@49:     virtual Return operator()(Params... params) const = 0;
cannam@49:   };
cannam@49: 
cannam@49:   template <typename F>
cannam@49:   class Impl final: public Iface {
cannam@49:   public:
cannam@49:     explicit Impl(F&& f): f(kj::fwd<F>(f)) {}
cannam@49: 
cannam@49:     Return operator()(Params... params) const override {
cannam@49:       return f(kj::fwd<Params>(params)...);
cannam@49:     }
cannam@49: 
cannam@49:   private:
cannam@49:     F f;
cannam@49:   };
cannam@49: 
cannam@49:   Own<Iface> impl;
cannam@49: };
cannam@49: 
cannam@49: #if 1
cannam@49: 
cannam@49: namespace _ {  // private
cannam@49: 
cannam@49: template <typename T, typename Signature, Signature method>
cannam@49: class BoundMethod;
cannam@49: 
cannam@49: template <typename T, typename Return, typename... Params, Return (Decay<T>::*method)(Params...)>
cannam@49: class BoundMethod<T, Return (Decay<T>::*)(Params...), method> {
cannam@49: public:
cannam@49:   BoundMethod(T&& t): t(kj::fwd<T>(t)) {}
cannam@49: 
cannam@49:   Return operator()(Params&&... params) {
cannam@49:     return (t.*method)(kj::fwd<Params>(params)...);
cannam@49:   }
cannam@49: 
cannam@49: private:
cannam@49:   T t;
cannam@49: };
cannam@49: 
cannam@49: template <typename T, typename Return, typename... Params,
cannam@49:           Return (Decay<T>::*method)(Params...) const>
cannam@49: class BoundMethod<T, Return (Decay<T>::*)(Params...) const, method> {
cannam@49: public:
cannam@49:   BoundMethod(T&& t): t(kj::fwd<T>(t)) {}
cannam@49: 
cannam@49:   Return operator()(Params&&... params) const {
cannam@49:     return (t.*method)(kj::fwd<Params>(params)...);
cannam@49:   }
cannam@49: 
cannam@49: private:
cannam@49:   T t;
cannam@49: };
cannam@49: 
cannam@49: }  // namespace _ (private)
cannam@49: 
cannam@49: #define KJ_BIND_METHOD(obj, method) \
cannam@49:   ::kj::_::BoundMethod<KJ_DECLTYPE_REF(obj), \
cannam@49:                        decltype(&::kj::Decay<decltype(obj)>::method), \
cannam@49:                        &::kj::Decay<decltype(obj)>::method>(obj)
cannam@49: // Macro that produces a functor object which forwards to the method `obj.name`.  If `obj` is an
cannam@49: // lvalue, the functor will hold a reference to it.  If `obj` is an rvalue, the functor will
cannam@49: // contain a copy (by move) of it.
cannam@49: //
cannam@49: // The current implementation requires that the method is not overloaded.
cannam@49: //
cannam@49: // TODO(someday):  C++14's generic lambdas may be able to simplify this code considerably, and
cannam@49: //   probably make it work with overloaded methods.
cannam@49: 
cannam@49: #else
cannam@49: // Here's a better implementation of the above that doesn't work with GCC (but does with Clang)
cannam@49: // because it uses a local class with a template method.  Sigh.  This implementation supports
cannam@49: // overloaded methods.
cannam@49: 
cannam@49: #define KJ_BIND_METHOD(obj, method) \
cannam@49:   ({ \
cannam@49:     typedef KJ_DECLTYPE_REF(obj) T; \
cannam@49:     class F { \
cannam@49:     public: \
cannam@49:       inline F(T&& t): t(::kj::fwd<T>(t)) {} \
cannam@49:       template <typename... Params> \
cannam@49:       auto operator()(Params&&... params) \
cannam@49:           -> decltype(::kj::instance<T>().method(::kj::fwd<Params>(params)...)) { \
cannam@49:         return t.method(::kj::fwd<Params>(params)...); \
cannam@49:       } \
cannam@49:     private: \
cannam@49:       T t; \
cannam@49:     }; \
cannam@49:     (F(obj)); \
cannam@49:   })
cannam@49: // Macro that produces a functor object which forwards to the method `obj.name`.  If `obj` is an
cannam@49: // lvalue, the functor will hold a reference to it.  If `obj` is an rvalue, the functor will
cannam@49: // contain a copy (by move) of it.
cannam@49: 
cannam@49: #endif
cannam@49: 
cannam@49: }  // namespace kj
cannam@49: 
cannam@49: #endif  // KJ_FUNCTION_H_