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// Copyright (c) 2013, Kenton Varda <temporal@gmail.com>
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this
// list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
// ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#ifndef KJ_FUNCTION_H_
#define KJ_FUNCTION_H_
#include "memory.h"
namespace kj {
template <typename Signature>
class Function;
// Function wrapper using virtual-based polymorphism. Use this when template polymorphism is
// not possible. You can, for example, accept a Function as a parameter:
//
// void setFilter(Function<bool(const Widget&)> filter);
//
// The caller of `setFilter()` may then pass any callable object as the parameter. The callable
// object does not have to have the exact signature specified, just one that is "compatible" --
// i.e. the return type is covariant and the parameters are contravariant.
//
// Unlike `std::function`, `kj::Function`s are movable but not copyable, just like `kj::Own`. This
// is to avoid unexpected heap allocation or slow atomic reference counting.
//
// When a `Function` is constructed from an lvalue, it captures only a reference to the value.
// When constructed from an rvalue, it invokes the value's move constructor. So, for example:
//
// struct AddN {
// int n;
// int operator(int i) { return i + n; }
// }
//
// Function<int(int, int)> f1 = AddN{2};
// // f1 owns an instance of AddN. It may safely be moved out
// // of the local scope.
//
// AddN adder(2);
// Function<int(int, int)> f2 = adder;
// // f2 contains a reference to `adder`. Thus, it becomes invalid
// // when `adder` goes out-of-scope.
//
// AddN adder2(2);
// Function<int(int, int)> f3 = kj::mv(adder2);
// // f3 owns an insatnce of AddN moved from `adder2`. f3 may safely
// // be moved out of the local scope.
//
// Additionally, a Function may be bound to a class method using KJ_BIND_METHOD(object, methodName).
// For example:
//
// class Printer {
// public:
// void print(int i);
// void print(kj::StringPtr s);
// };
//
// Printer p;
//
// Function<void(uint)> intPrinter = KJ_BIND_METHOD(p, print);
// // Will call Printer::print(int).
//
// Function<void(const char*)> strPrinter = KJ_BIND_METHOD(p, print);
// // Will call Printer::print(kj::StringPtr).
//
// Notice how KJ_BIND_METHOD is able to figure out which overload to use depending on the kind of
// Function it is binding to.
template <typename Return, typename... Params>
class Function<Return(Params...)> {
public:
template <typename F>
inline Function(F&& f): impl(heap<Impl<F>>(kj::fwd<F>(f))) {}
Function() = default;
inline Return operator()(Params... params) {
return (*impl)(kj::fwd<Params>(params)...);
}
private:
class Iface {
public:
virtual Return operator()(Params... params) = 0;
};
template <typename F>
class Impl final: public Iface {
public:
explicit Impl(F&& f): f(kj::fwd<F>(f)) {}
Return operator()(Params... params) override {
return f(kj::fwd<Params>(params)...);
}
private:
F f;
};
Own<Iface> impl;
};
namespace _ { // private
template <typename T>
T rvalueOrRef(T&&);
// Hack to help detect if an expression is an lvalue or an rvalue.
//
// int i;
// decltype(i) i1(i); // i1 has type int.
// decltype(rvalueOrRef(i)) i2(i); // i2 has type int&.
// decltype(rvalueOrRef(kj::mv(i)) i3(kj::mv(i)); // i3 has type int.
} // namespace _ (private)
#if 1
namespace _ { // private
template <typename T, typename Signature, Signature method>
class BoundMethod;
template <typename T, typename Return, typename... Params, Return (Decay<T>::*method)(Params...)>
class BoundMethod<T, Return (Decay<T>::*)(Params...), method> {
public:
BoundMethod(T&& t): t(kj::fwd<T>(t)) {}
Return operator()(Params&&... params) {
return (t.*method)(kj::fwd<Params>(params)...);
}
private:
T t;
};
} // namespace _ (private)
#define KJ_BIND_METHOD(obj, method) \
::kj::_::BoundMethod<decltype(::kj::_::rvalueOrRef(obj)), \
decltype(&::kj::Decay<decltype(obj)>::method), \
&::kj::Decay<decltype(obj)>::method>(obj)
// Macro that produces a functor object which forwards to the method `obj.name`. If `obj` is an
// lvalue, the functor will hold a reference to it. If `obj` is an rvalue, the functor will
// contain a copy (by move) of it.
//
// The current implementation requires that the method is not overloaded.
//
// TODO(someday): C++14's generic lambdas may be able to simplify this code considerably, and
// probably make it work with overloaded methods.
#else
// Here's a better implementation of the above that doesn't work with GCC (but does with Clang)
// because it uses a local class with a template method. Sigh. This implementation supports
// overloaded methods.
#define KJ_BIND_METHOD(obj, method) \
({ \
typedef decltype(::kj::_::rvalueOrRef(obj)) T; \
class F { \
public: \
inline F(T&& t): t(::kj::fwd<T>(t)) {} \
template <typename... Params> \
auto operator()(Params&&... params) \
-> decltype(::kj::instance<T>().method(::kj::fwd<Params>(params)...)) { \
return t.method(::kj::fwd<Params>(params)...); \
} \
private: \
T t; \
}; \
(F(obj)); \
})
// Macro that produces a functor object which forwards to the method `obj.name`. If `obj` is an
// lvalue, the functor will hold a reference to it. If `obj` is an rvalue, the functor will
// contain a copy (by move) of it.
#endif
} // namespace kj
#endif // KJ_FUNCTION_H_