| // Boost Lambda Library -- if.hpp ------------------------------------------ |
| |
| // Copyright (C) 1999, 2000 Jaakko Jarvi (jaakko.jarvi@cs.utu.fi) |
| // Copyright (C) 2000 Gary Powell (powellg@amazon.com) |
| // Copyright (C) 2001-2002 Joel de Guzman |
| // |
| // Distributed under the Boost Software License, Version 1.0. (See |
| // accompanying file LICENSE_1_0.txt or copy at |
| // http://www.boost.org/LICENSE_1_0.txt) |
| // |
| // For more information, see www.boost.org |
| |
| // -------------------------------------------------------------------------- |
| |
| #if !defined(BOOST_LAMBDA_IF_HPP) |
| #define BOOST_LAMBDA_IF_HPP |
| |
| #include "boost/lambda/core.hpp" |
| |
| // Arithmetic type promotion needed for if_then_else_return |
| #include "boost/lambda/detail/operator_actions.hpp" |
| #include "boost/lambda/detail/operator_return_type_traits.hpp" |
| |
| namespace boost { |
| namespace lambda { |
| |
| // -- if control construct actions ---------------------- |
| |
| class ifthen_action {}; |
| class ifthenelse_action {}; |
| class ifthenelsereturn_action {}; |
| |
| // Specialization for if_then. |
| template<class Args> |
| class |
| lambda_functor_base<ifthen_action, Args> { |
| public: |
| Args args; |
| template <class T> struct sig { typedef void type; }; |
| public: |
| explicit lambda_functor_base(const Args& a) : args(a) {} |
| |
| template<class RET, CALL_TEMPLATE_ARGS> |
| RET call(CALL_FORMAL_ARGS) const { |
| if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) |
| detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); |
| } |
| }; |
| |
| // If Then |
| template <class Arg1, class Arg2> |
| inline const |
| lambda_functor< |
| lambda_functor_base< |
| ifthen_action, |
| tuple<lambda_functor<Arg1>, lambda_functor<Arg2> > |
| > |
| > |
| if_then(const lambda_functor<Arg1>& a1, const lambda_functor<Arg2>& a2) { |
| return |
| lambda_functor_base< |
| ifthen_action, |
| tuple<lambda_functor<Arg1>, lambda_functor<Arg2> > |
| > |
| ( tuple<lambda_functor<Arg1>, lambda_functor<Arg2> >(a1, a2) ); |
| } |
| |
| |
| // Specialization for if_then_else. |
| template<class Args> |
| class |
| lambda_functor_base<ifthenelse_action, Args> { |
| public: |
| Args args; |
| template <class T> struct sig { typedef void type; }; |
| public: |
| explicit lambda_functor_base(const Args& a) : args(a) {} |
| |
| template<class RET, CALL_TEMPLATE_ARGS> |
| RET call(CALL_FORMAL_ARGS) const { |
| if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) |
| detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); |
| else |
| detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS); |
| } |
| }; |
| |
| |
| |
| // If then else |
| |
| template <class Arg1, class Arg2, class Arg3> |
| inline const |
| lambda_functor< |
| lambda_functor_base< |
| ifthenelse_action, |
| tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> > |
| > |
| > |
| if_then_else(const lambda_functor<Arg1>& a1, const lambda_functor<Arg2>& a2, |
| const lambda_functor<Arg3>& a3) { |
| return |
| lambda_functor_base< |
| ifthenelse_action, |
| tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> > |
| > |
| (tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> > |
| (a1, a2, a3) ); |
| } |
| |
| // Our version of operator?:() |
| |
| template <class Arg1, class Arg2, class Arg3> |
| inline const |
| lambda_functor< |
| lambda_functor_base< |
| other_action<ifthenelsereturn_action>, |
| tuple<lambda_functor<Arg1>, |
| typename const_copy_argument<Arg2>::type, |
| typename const_copy_argument<Arg3>::type> |
| > |
| > |
| if_then_else_return(const lambda_functor<Arg1>& a1, |
| const Arg2 & a2, |
| const Arg3 & a3) { |
| return |
| lambda_functor_base< |
| other_action<ifthenelsereturn_action>, |
| tuple<lambda_functor<Arg1>, |
| typename const_copy_argument<Arg2>::type, |
| typename const_copy_argument<Arg3>::type> |
| > ( tuple<lambda_functor<Arg1>, |
| typename const_copy_argument<Arg2>::type, |
| typename const_copy_argument<Arg3>::type> (a1, a2, a3) ); |
| } |
| |
| namespace detail { |
| |
| // return type specialization for conditional expression begins ----------- |
| // start reading below and move upwards |
| |
| // PHASE 6:1 |
| // check if A is conbertible to B and B to A |
| template<int Phase, bool AtoB, bool BtoA, bool SameType, class A, class B> |
| struct return_type_2_ifthenelsereturn; |
| |
| // if A can be converted to B and vice versa -> ambiguous |
| template<int Phase, class A, class B> |
| struct return_type_2_ifthenelsereturn<Phase, true, true, false, A, B> { |
| typedef |
| detail::return_type_deduction_failure<return_type_2_ifthenelsereturn> type; |
| // ambiguous type in conditional expression |
| }; |
| // if A can be converted to B and vice versa and are of same type |
| template<int Phase, class A, class B> |
| struct return_type_2_ifthenelsereturn<Phase, true, true, true, A, B> { |
| typedef A type; |
| }; |
| |
| |
| // A can be converted to B |
| template<int Phase, class A, class B> |
| struct return_type_2_ifthenelsereturn<Phase, true, false, false, A, B> { |
| typedef B type; |
| }; |
| |
| // B can be converted to A |
| template<int Phase, class A, class B> |
| struct return_type_2_ifthenelsereturn<Phase, false, true, false, A, B> { |
| typedef A type; |
| }; |
| |
| // neither can be converted. Then we drop the potential references, and |
| // try again |
| template<class A, class B> |
| struct return_type_2_ifthenelsereturn<1, false, false, false, A, B> { |
| // it is safe to add const, since the result will be an rvalue and thus |
| // const anyway. The const are needed eg. if the types |
| // are 'const int*' and 'void *'. The remaining type should be 'const void*' |
| typedef const typename boost::remove_reference<A>::type plainA; |
| typedef const typename boost::remove_reference<B>::type plainB; |
| // TODO: Add support for volatile ? |
| |
| typedef typename |
| return_type_2_ifthenelsereturn< |
| 2, |
| boost::is_convertible<plainA,plainB>::value, |
| boost::is_convertible<plainB,plainA>::value, |
| boost::is_same<plainA,plainB>::value, |
| plainA, |
| plainB>::type type; |
| }; |
| |
| // PHASE 6:2 |
| template<class A, class B> |
| struct return_type_2_ifthenelsereturn<2, false, false, false, A, B> { |
| typedef |
| detail::return_type_deduction_failure<return_type_2_ifthenelsereturn> type; |
| // types_do_not_match_in_conditional_expression |
| }; |
| |
| |
| |
| // PHASE 5: now we know that types are not arithmetic. |
| template<class A, class B> |
| struct non_numeric_types { |
| typedef typename |
| return_type_2_ifthenelsereturn< |
| 1, // phase 1 |
| is_convertible<A,B>::value, |
| is_convertible<B,A>::value, |
| is_same<A,B>::value, |
| A, |
| B>::type type; |
| }; |
| |
| // PHASE 4 : |
| // the base case covers arithmetic types with differing promote codes |
| // use the type deduction of arithmetic_actions |
| template<int CodeA, int CodeB, class A, class B> |
| struct arithmetic_or_not { |
| typedef typename |
| return_type_2<arithmetic_action<plus_action>, A, B>::type type; |
| // plus_action is just a random pick, has to be a concrete instance |
| }; |
| |
| // this case covers the case of artihmetic types with the same promote codes. |
| // non numeric deduction is used since e.g. integral promotion is not |
| // performed with operator ?: |
| template<int CodeA, class A, class B> |
| struct arithmetic_or_not<CodeA, CodeA, A, B> { |
| typedef typename non_numeric_types<A, B>::type type; |
| }; |
| |
| // if either A or B has promote code -1 it is not an arithmetic type |
| template<class A, class B> |
| struct arithmetic_or_not <-1, -1, A, B> { |
| typedef typename non_numeric_types<A, B>::type type; |
| }; |
| template<int CodeB, class A, class B> |
| struct arithmetic_or_not <-1, CodeB, A, B> { |
| typedef typename non_numeric_types<A, B>::type type; |
| }; |
| template<int CodeA, class A, class B> |
| struct arithmetic_or_not <CodeA, -1, A, B> { |
| typedef typename non_numeric_types<A, B>::type type; |
| }; |
| |
| |
| |
| |
| // PHASE 3 : Are the types same? |
| // No, check if they are arithmetic or not |
| template <class A, class B> |
| struct same_or_not { |
| typedef typename detail::remove_reference_and_cv<A>::type plainA; |
| typedef typename detail::remove_reference_and_cv<B>::type plainB; |
| |
| typedef typename |
| arithmetic_or_not< |
| detail::promote_code<plainA>::value, |
| detail::promote_code<plainB>::value, |
| A, |
| B>::type type; |
| }; |
| // Yes, clear. |
| template <class A> struct same_or_not<A, A> { |
| typedef A type; |
| }; |
| |
| } // detail |
| |
| // PHASE 2 : Perform first the potential array_to_pointer conversion |
| template<class A, class B> |
| struct return_type_2<other_action<ifthenelsereturn_action>, A, B> { |
| |
| typedef typename detail::array_to_pointer<A>::type A1; |
| typedef typename detail::array_to_pointer<B>::type B1; |
| |
| typedef typename |
| boost::add_const<typename detail::same_or_not<A1, B1>::type>::type type; |
| }; |
| |
| // PHASE 1 : Deduction is based on the second and third operand |
| |
| |
| // return type specialization for conditional expression ends ----------- |
| |
| |
| // Specialization of lambda_functor_base for if_then_else_return. |
| template<class Args> |
| class |
| lambda_functor_base<other_action<ifthenelsereturn_action>, Args> { |
| public: |
| Args args; |
| |
| template <class SigArgs> struct sig { |
| private: |
| typedef typename detail::nth_return_type_sig<1, Args, SigArgs>::type ret1; |
| typedef typename detail::nth_return_type_sig<2, Args, SigArgs>::type ret2; |
| public: |
| typedef typename return_type_2< |
| other_action<ifthenelsereturn_action>, ret1, ret2 |
| >::type type; |
| }; |
| |
| public: |
| explicit lambda_functor_base(const Args& a) : args(a) {} |
| |
| template<class RET, CALL_TEMPLATE_ARGS> |
| RET call(CALL_FORMAL_ARGS) const { |
| return (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) ? |
| detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS) |
| : |
| detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS); |
| } |
| }; |
| |
| // The code below is from Joel de Guzman, some name changes etc. |
| // has been made. |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| // |
| // if_then_else_composite |
| // |
| // This composite has two (2) forms: |
| // |
| // if_(condition) |
| // [ |
| // statement |
| // ] |
| // |
| // and |
| // |
| // if_(condition) |
| // [ |
| // true_statement |
| // ] |
| // .else_ |
| // [ |
| // false_statement |
| // ] |
| // |
| // where condition is an lambda_functor that evaluates to bool. If condition |
| // is true, the true_statement (again an lambda_functor) is executed |
| // otherwise, the false_statement (another lambda_functor) is executed. The |
| // result type of this is void. Note the trailing underscore after |
| // if_ and the the leading dot and the trailing underscore before |
| // and after .else_. |
| // |
| /////////////////////////////////////////////////////////////////////////////// |
| template <typename CondT, typename ThenT, typename ElseT> |
| struct if_then_else_composite { |
| |
| typedef if_then_else_composite<CondT, ThenT, ElseT> self_t; |
| |
| template <class SigArgs> |
| struct sig { typedef void type; }; |
| |
| if_then_else_composite( |
| CondT const& cond_, |
| ThenT const& then_, |
| ElseT const& else__) |
| : cond(cond_), then(then_), else_(else__) {} |
| |
| template <class Ret, CALL_TEMPLATE_ARGS> |
| Ret call(CALL_FORMAL_ARGS) const |
| { |
| if (cond.internal_call(CALL_ACTUAL_ARGS)) |
| then.internal_call(CALL_ACTUAL_ARGS); |
| else |
| else_.internal_call(CALL_ACTUAL_ARGS); |
| } |
| |
| CondT cond; ThenT then; ElseT else_; // lambda_functors |
| }; |
| |
| ////////////////////////////////// |
| template <typename CondT, typename ThenT> |
| struct else_gen { |
| |
| else_gen(CondT const& cond_, ThenT const& then_) |
| : cond(cond_), then(then_) {} |
| |
| template <typename ElseT> |
| lambda_functor<if_then_else_composite<CondT, ThenT, |
| typename as_lambda_functor<ElseT>::type> > |
| operator[](ElseT const& else_) |
| { |
| typedef if_then_else_composite<CondT, ThenT, |
| typename as_lambda_functor<ElseT>::type> |
| result; |
| |
| return result(cond, then, to_lambda_functor(else_)); |
| } |
| |
| CondT cond; ThenT then; |
| }; |
| |
| ////////////////////////////////// |
| template <typename CondT, typename ThenT> |
| struct if_then_composite { |
| |
| template <class SigArgs> |
| struct sig { typedef void type; }; |
| |
| if_then_composite(CondT const& cond_, ThenT const& then_) |
| : cond(cond_), then(then_), else_(cond, then) {} |
| |
| template <class Ret, CALL_TEMPLATE_ARGS> |
| Ret call(CALL_FORMAL_ARGS) const |
| { |
| if (cond.internal_call(CALL_ACTUAL_ARGS)) |
| then.internal_call(CALL_ACTUAL_ARGS); |
| } |
| |
| CondT cond; ThenT then; // lambda_functors |
| else_gen<CondT, ThenT> else_; |
| }; |
| |
| ////////////////////////////////// |
| template <typename CondT> |
| struct if_gen { |
| |
| if_gen(CondT const& cond_) |
| : cond(cond_) {} |
| |
| template <typename ThenT> |
| lambda_functor<if_then_composite< |
| typename as_lambda_functor<CondT>::type, |
| typename as_lambda_functor<ThenT>::type> > |
| operator[](ThenT const& then) const |
| { |
| typedef if_then_composite< |
| typename as_lambda_functor<CondT>::type, |
| typename as_lambda_functor<ThenT>::type> |
| result; |
| |
| return result( |
| to_lambda_functor(cond), |
| to_lambda_functor(then)); |
| } |
| |
| CondT cond; |
| }; |
| |
| ////////////////////////////////// |
| template <typename CondT> |
| inline if_gen<CondT> |
| if_(CondT const& cond) |
| { |
| return if_gen<CondT>(cond); |
| } |
| |
| |
| |
| } // lambda |
| } // boost |
| |
| #endif // BOOST_LAMBDA_IF_HPP |
| |
| |