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325 lines
10 KiB
325 lines
10 KiB
// Boost Lambda Library ret.hpp ----------------------------------------- |
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// Copyright (C) 1999, 2000 Jaakko Jarvi (jaakko.jarvi@cs.utu.fi) |
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// |
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// Distributed under the Boost Software License, Version 1.0. (See |
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// accompanying file LICENSE_1_0.txt or copy at |
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// http://www.boost.org/LICENSE_1_0.txt) |
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// |
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// For more information, see www.boost.org |
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#ifndef BOOST_LAMBDA_RET_HPP |
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#define BOOST_LAMBDA_RET_HPP |
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namespace boost { |
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namespace lambda { |
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// TODO: |
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// Add specializations for function references for ret, protect and unlambda |
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// e.g void foo(); unlambda(foo); fails, as it would add a const qualifier |
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// for a function type. |
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// on the other hand unlambda(*foo) does work |
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// -- ret ------------------------- |
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// the explicit return type template |
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// TODO: It'd be nice to make ret a nop for other than lambda functors |
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// but causes an ambiguiyty with gcc (not with KCC), check what is the |
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// right interpretation. |
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// // ret for others than lambda functors has no effect |
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// template <class U, class T> |
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// inline const T& ret(const T& t) { return t; } |
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template<class RET, class Arg> |
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inline const |
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lambda_functor< |
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lambda_functor_base< |
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explicit_return_type_action<RET>, |
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tuple<lambda_functor<Arg> > |
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> |
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> |
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ret(const lambda_functor<Arg>& a1) |
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{ |
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return |
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lambda_functor_base< |
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explicit_return_type_action<RET>, |
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tuple<lambda_functor<Arg> > |
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> |
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(tuple<lambda_functor<Arg> >(a1)); |
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} |
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// protect ------------------ |
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// protecting others than lambda functors has no effect |
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template <class T> |
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inline const T& protect(const T& t) { return t; } |
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template<class Arg> |
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inline const |
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lambda_functor< |
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lambda_functor_base< |
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protect_action, |
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tuple<lambda_functor<Arg> > |
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> |
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> |
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protect(const lambda_functor<Arg>& a1) |
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{ |
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return |
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lambda_functor_base< |
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protect_action, |
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tuple<lambda_functor<Arg> > |
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> |
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(tuple<lambda_functor<Arg> >(a1)); |
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} |
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// ------------------------------------------------------------------- |
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// Hides the lambda functorness of a lambda functor. |
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// After this, the functor is immune to argument substitution, etc. |
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// This can be used, e.g. to make it safe to pass lambda functors as |
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// arguments to functions, which might use them as target functions |
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// note, unlambda and protect are different things. Protect hides the lambda |
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// functor for one application, unlambda for good. |
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template <class LambdaFunctor> |
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class non_lambda_functor |
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{ |
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LambdaFunctor lf; |
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public: |
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// This functor defines the result_type typedef. |
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// The result type must be deducible without knowing the arguments |
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template <class SigArgs> struct sig { |
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typedef typename |
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LambdaFunctor::inherited:: |
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template sig<typename SigArgs::tail_type>::type type; |
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}; |
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explicit non_lambda_functor(const LambdaFunctor& a) : lf(a) {} |
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typename LambdaFunctor::nullary_return_type |
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operator()() const { |
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return lf.template |
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call<typename LambdaFunctor::nullary_return_type> |
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(cnull_type(), cnull_type(), cnull_type(), cnull_type()); |
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} |
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template<class A> |
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typename sig<tuple<const non_lambda_functor, A&> >::type |
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operator()(A& a) const { |
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return lf.template call<typename sig<tuple<const non_lambda_functor, A&> >::type >(a, cnull_type(), cnull_type(), cnull_type()); |
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} |
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template<class A, class B> |
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typename sig<tuple<const non_lambda_functor, A&, B&> >::type |
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operator()(A& a, B& b) const { |
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return lf.template call<typename sig<tuple<const non_lambda_functor, A&, B&> >::type >(a, b, cnull_type(), cnull_type()); |
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} |
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template<class A, class B, class C> |
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typename sig<tuple<const non_lambda_functor, A&, B&, C&> >::type |
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operator()(A& a, B& b, C& c) const { |
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return lf.template call<typename sig<tuple<const non_lambda_functor, A&, B&, C&> >::type>(a, b, c, cnull_type()); |
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} |
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}; |
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template <class Arg> |
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inline const Arg& unlambda(const Arg& a) { return a; } |
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template <class Arg> |
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inline const non_lambda_functor<lambda_functor<Arg> > |
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unlambda(const lambda_functor<Arg>& a) |
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{ |
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return non_lambda_functor<lambda_functor<Arg> >(a); |
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} |
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// Due to a language restriction, lambda functors cannot be made to |
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// accept non-const rvalue arguments. Usually iterators do not return |
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// temporaries, but sometimes they do. That's why a workaround is provided. |
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// Note, that this potentially breaks const correctness, so be careful! |
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// any lambda functor can be turned into a const_incorrect_lambda_functor |
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// The operator() takes arguments as consts and then casts constness |
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// away. So this breaks const correctness!!! but is a necessary workaround |
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// in some cases due to language limitations. |
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// Note, that this is not a lambda_functor anymore, so it can not be used |
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// as a sub lambda expression. |
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template <class LambdaFunctor> |
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struct const_incorrect_lambda_functor { |
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LambdaFunctor lf; |
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public: |
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explicit const_incorrect_lambda_functor(const LambdaFunctor& a) : lf(a) {} |
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template <class SigArgs> struct sig { |
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typedef typename |
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LambdaFunctor::inherited::template |
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sig<typename SigArgs::tail_type>::type type; |
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}; |
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// The nullary case is not needed (no arguments, no parameter type problems) |
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template<class A> |
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typename sig<tuple<const const_incorrect_lambda_functor, A&> >::type |
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operator()(const A& a) const { |
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return lf.template call<typename sig<tuple<const const_incorrect_lambda_functor, A&> >::type >(const_cast<A&>(a), cnull_type(), cnull_type(), cnull_type()); |
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} |
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template<class A, class B> |
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typename sig<tuple<const const_incorrect_lambda_functor, A&, B&> >::type |
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operator()(const A& a, const B& b) const { |
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return lf.template call<typename sig<tuple<const const_incorrect_lambda_functor, A&, B&> >::type >(const_cast<A&>(a), const_cast<B&>(b), cnull_type(), cnull_type()); |
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} |
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template<class A, class B, class C> |
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typename sig<tuple<const const_incorrect_lambda_functor, A&, B&, C&> >::type |
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operator()(const A& a, const B& b, const C& c) const { |
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return lf.template call<typename sig<tuple<const const_incorrect_lambda_functor, A&, B&, C&> >::type>(const_cast<A&>(a), const_cast<B&>(b), const_cast<C&>(c), cnull_type()); |
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} |
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}; |
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// ------------------------------------------------------------------------ |
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// any lambda functor can be turned into a const_parameter_lambda_functor |
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// The operator() takes arguments as const. |
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// This is useful if lambda functors are called with non-const rvalues. |
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// Note, that this is not a lambda_functor anymore, so it can not be used |
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// as a sub lambda expression. |
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template <class LambdaFunctor> |
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struct const_parameter_lambda_functor { |
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LambdaFunctor lf; |
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public: |
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explicit const_parameter_lambda_functor(const LambdaFunctor& a) : lf(a) {} |
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template <class SigArgs> struct sig { |
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typedef typename |
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LambdaFunctor::inherited::template |
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sig<typename SigArgs::tail_type>::type type; |
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}; |
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// The nullary case is not needed: no arguments, no constness problems. |
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template<class A> |
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typename sig<tuple<const const_parameter_lambda_functor, const A&> >::type |
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operator()(const A& a) const { |
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return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&> >::type >(a, cnull_type(), cnull_type(), cnull_type()); |
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} |
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template<class A, class B> |
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typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&> >::type |
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operator()(const A& a, const B& b) const { |
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return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&> >::type >(a, b, cnull_type(), cnull_type()); |
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} |
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template<class A, class B, class C> |
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typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&, const C&> |
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>::type |
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operator()(const A& a, const B& b, const C& c) const { |
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return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&, const C&> >::type>(a, b, c, cnull_type()); |
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} |
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}; |
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template <class Arg> |
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inline const const_incorrect_lambda_functor<lambda_functor<Arg> > |
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break_const(const lambda_functor<Arg>& lf) |
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{ |
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return const_incorrect_lambda_functor<lambda_functor<Arg> >(lf); |
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} |
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template <class Arg> |
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inline const const_parameter_lambda_functor<lambda_functor<Arg> > |
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const_parameters(const lambda_functor<Arg>& lf) |
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{ |
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return const_parameter_lambda_functor<lambda_functor<Arg> >(lf); |
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} |
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// make void ------------------------------------------------ |
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// make_void( x ) turns a lambda functor x with some return type y into |
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// another lambda functor, which has a void return type |
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// when called, the original return type is discarded |
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// we use this action. The action class will be called, which means that |
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// the wrapped lambda functor is evaluated, but we just don't do anything |
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// with the result. |
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struct voidifier_action { |
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template<class Ret, class A> static void apply(A&) {} |
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}; |
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template<class Args> struct return_type_N<voidifier_action, Args> { |
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typedef void type; |
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}; |
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template<class Arg1> |
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inline const |
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lambda_functor< |
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lambda_functor_base< |
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action<1, voidifier_action>, |
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tuple<lambda_functor<Arg1> > |
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> |
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> |
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make_void(const lambda_functor<Arg1>& a1) { |
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return |
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lambda_functor_base< |
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action<1, voidifier_action>, |
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tuple<lambda_functor<Arg1> > |
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> |
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(tuple<lambda_functor<Arg1> > (a1)); |
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} |
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// for non-lambda functors, make_void does nothing |
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// (the argument gets evaluated immediately) |
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template<class Arg1> |
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inline const |
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lambda_functor< |
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lambda_functor_base<do_nothing_action, null_type> |
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> |
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make_void(const Arg1& a1) { |
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return |
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lambda_functor_base<do_nothing_action, null_type>(); |
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} |
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// std_functor ----------------------------------------------------- |
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// The STL uses the result_type typedef as the convention to let binders know |
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// the return type of a function object. |
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// LL uses the sig template. |
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// To let LL know that the function object has the result_type typedef |
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// defined, it can be wrapped with the std_functor function. |
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// Just inherit form the template parameter (the standard functor), |
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// and provide a sig template. So we have a class which is still the |
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// same functor + the sig template. |
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template<class T> |
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struct result_type_to_sig : public T { |
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template<class Args> struct sig { typedef typename T::result_type type; }; |
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result_type_to_sig(const T& t) : T(t) {} |
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}; |
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template<class F> |
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inline result_type_to_sig<F> std_functor(const F& f) { return f; } |
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} // namespace lambda |
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} // namespace boost |
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#endif |
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