comparison osx/include/kj/function.h @ 134:41e769c91eca

Add Capnp and KJ builds for OSX

+// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
+// Licensed under the MIT License:
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+#ifndef KJ_FUNCTION_H_
+#define KJ_FUNCTION_H_
+
+#if defined(__GNUC__) && !KJ_HEADER_WARNINGS
+#pragma GCC system_header
+#endif
+
+#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 Signature>
+class ConstFunction;
+// Like Function, but wraps a "const" (i.e. thread-safe) call.
+
+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;
+
+  // Make sure people don't accidentally end up wrapping a reference when they meant to return
+  // a function.
+  KJ_DISALLOW_COPY(Function);
+  Function(Function&) = delete;
+  Function& operator=(Function&) = delete;
+  template <typename T> Function(const Function<T>&) = delete;
+  template <typename T> Function& operator=(const Function<T>&) = delete;
+  template <typename T> Function(const ConstFunction<T>&) = delete;
+  template <typename T> Function& operator=(const ConstFunction<T>&) = delete;
+  Function(Function&&) = default;
+  Function& operator=(Function&&) = default;
+
+  inline Return operator()(Params... params) {
+    return (*impl)(kj::fwd<Params>(params)...);
+  }
+
+  Function reference() {
+    // Forms a new Function of the same type that delegates to this Function by reference.
+    // Therefore, this Function must outlive the returned Function, but otherwise they behave
+    // exactly the same.
+
+    return *impl;
+  }
+
+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;
+};
+
+template <typename Return, typename... Params>
+class ConstFunction<Return(Params...)> {
+public:
+  template <typename F>
+  inline ConstFunction(F&& f): impl(heap<Impl<F>>(kj::fwd<F>(f))) {}
+  ConstFunction() = default;
+
+  // Make sure people don't accidentally end up wrapping a reference when they meant to return
+  // a function.
+  KJ_DISALLOW_COPY(ConstFunction);
+  ConstFunction(ConstFunction&) = delete;
+  ConstFunction& operator=(ConstFunction&) = delete;
+  template <typename T> ConstFunction(const ConstFunction<T>&) = delete;
+  template <typename T> ConstFunction& operator=(const ConstFunction<T>&) = delete;
+  template <typename T> ConstFunction(const Function<T>&) = delete;
+  template <typename T> ConstFunction& operator=(const Function<T>&) = delete;
+  ConstFunction(ConstFunction&&) = default;
+  ConstFunction& operator=(ConstFunction&&) = default;
+
+  inline Return operator()(Params... params) const {
+    return (*impl)(kj::fwd<Params>(params)...);
+  }
+
+  ConstFunction reference() const {
+    // Forms a new ConstFunction of the same type that delegates to this ConstFunction by reference.
+    // Therefore, this ConstFunction must outlive the returned ConstFunction, but otherwise they
+    // behave exactly the same.
+
+    return *impl;
+  }
+
+private:
+  class Iface {
+  public:
+    virtual Return operator()(Params... params) const = 0;
+  };
+
+  template <typename F>
+  class Impl final: public Iface {
+  public:
+    explicit Impl(F&& f): f(kj::fwd<F>(f)) {}
+
+    Return operator()(Params... params) const override {
+      return f(kj::fwd<Params>(params)...);
+    }
+
+  private:
+    F f;
+  };
+
+  Own<Iface> impl;
+};
+
+#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;
+};
+
+template <typename T, typename Return, typename... Params,
+          Return (Decay<T>::*method)(Params...) const>
+class BoundMethod<T, Return (Decay<T>::*)(Params...) const, method> {
+public:
+  BoundMethod(T&& t): t(kj::fwd<T>(t)) {}
+
+  Return operator()(Params&&... params) const {
+    return (t.*method)(kj::fwd<Params>(params)...);
+  }
+
+private:
+  T t;
+};
+
+}  // namespace _ (private)
+
+#define KJ_BIND_METHOD(obj, method) \
+  ::kj::_::BoundMethod<KJ_DECLTYPE_REF(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 KJ_DECLTYPE_REF(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_