437 lines
13 KiB
Plaintext
437 lines
13 KiB
Plaintext
// Copyright Daniel Wallin, David Abrahams 2005. Use, modification and
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// distribution is subject to 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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#ifndef ARG_LIST_050329_HPP
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#define ARG_LIST_050329_HPP
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#include <boost/parameter/aux_/void.hpp>
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#include <boost/parameter/aux_/result_of0.hpp>
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#include <boost/parameter/aux_/default.hpp>
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#include <boost/parameter/aux_/parameter_requirements.hpp>
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#include <boost/parameter/aux_/yesno.hpp>
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#include <boost/parameter/aux_/is_maybe.hpp>
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#include <boost/parameter/config.hpp>
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#include <boost/mpl/apply.hpp>
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#include <boost/mpl/assert.hpp>
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#include <boost/mpl/begin.hpp>
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#include <boost/mpl/end.hpp>
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#include <boost/mpl/iterator_tags.hpp>
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#include <boost/type_traits/add_reference.hpp>
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#include <boost/type_traits/is_same.hpp>
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#include <boost/preprocessor/repetition/enum_params.hpp>
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#include <boost/preprocessor/repetition/enum_binary_params.hpp>
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#include <boost/preprocessor/facilities/intercept.hpp>
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namespace boost { namespace parameter {
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// Forward declaration for aux::arg_list, below.
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template<class T> struct keyword;
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namespace aux {
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// Tag type passed to MPL lambda.
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struct lambda_tag;
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//
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// Structures used to build the tuple of actual arguments. The
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// tuple is a nested cons-style list of arg_list specializations
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// terminated by an empty_arg_list.
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//
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// Each specialization of arg_list is derived from its successor in
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// the list type. This feature is used along with using
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// declarations to build member function overload sets that can
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// match against keywords.
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//
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// MPL sequence support
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struct arg_list_tag;
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// Terminates arg_list<> and represents an empty list. Since this
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// is just the terminating case you might want to look at arg_list
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// first, to get a feel for what's really happening here.
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struct empty_arg_list
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{
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empty_arg_list() {}
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// Constructor taking BOOST_PARAMETER_MAX_ARITY empty_arg_list
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// arguments; this makes initialization
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empty_arg_list(
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BOOST_PP_ENUM_PARAMS(
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BOOST_PARAMETER_MAX_ARITY, void_ BOOST_PP_INTERCEPT
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))
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{}
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// A metafunction class that, given a keyword and a default
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// type, returns the appropriate result type for a keyword
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// lookup given that default
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struct binding
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{
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template<class KW, class Default, class Reference>
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struct apply
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{
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typedef Default type;
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};
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};
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// Terminator for has_key, indicating that the keyword is unique
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template <class KW>
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static no_tag has_key(KW*);
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#if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
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// The overload set technique doesn't work with these older
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// compilers, so they need some explicit handholding.
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// A metafunction class that, given a keyword, returns the type
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// of the base sublist whose get() function can produce the
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// value for that key
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struct key_owner
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{
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template<class KW>
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struct apply
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{
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typedef empty_arg_list type;
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};
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};
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template <class K, class T>
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T& get(default_<K,T> x) const
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{
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return x.value;
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}
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template <class K, class F>
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typename result_of0<F>::type
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get(lazy_default<K,F> x) const
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{
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return x.compute_default();
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}
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#endif
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// If this function is called, it means there is no argument
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// in the list that matches the supplied keyword. Just return
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// the default value.
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template <class K, class Default>
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Default& operator[](default_<K, Default> x) const
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{
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return x.value;
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}
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// If this function is called, it means there is no argument
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// in the list that matches the supplied keyword. Just evaluate
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// and return the default value.
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template <class K, class F>
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typename result_of0<F>::type
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operator[](
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BOOST_PARAMETER_lazy_default_fallback<K,F> x) const
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{
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return x.compute_default();
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}
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// No argument corresponding to ParameterRequirements::key_type
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// was found if we match this overload, so unless that parameter
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// has a default, we indicate that the actual arguments don't
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// match the function's requirements.
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template <class ParameterRequirements, class ArgPack>
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static typename ParameterRequirements::has_default
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satisfies(ParameterRequirements*, ArgPack*);
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// MPL sequence support
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typedef empty_arg_list type; // convenience
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typedef arg_list_tag tag; // For dispatching to sequence intrinsics
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};
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// Forward declaration for arg_list::operator,
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template <class KW, class T>
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struct tagged_argument;
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template <class T>
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struct get_reference
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{
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typedef typename T::reference type;
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};
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// A tuple of tagged arguments, terminated with empty_arg_list.
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// Every TaggedArg is an instance of tagged_argument<>.
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template <class TaggedArg, class Next = empty_arg_list>
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struct arg_list : Next
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{
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typedef arg_list<TaggedArg,Next> self;
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typedef typename TaggedArg::key_type key_type;
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typedef typename is_maybe<typename TaggedArg::value_type>::type holds_maybe;
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typedef typename mpl::eval_if<
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holds_maybe
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, get_reference<typename TaggedArg::value_type>
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, get_reference<TaggedArg>
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>::type reference;
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typedef typename mpl::if_<
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holds_maybe
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, reference
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, typename TaggedArg::value_type
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>::type value_type;
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TaggedArg arg; // Stores the argument
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// Store the arguments in successive nodes of this list
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template< // class A0, class A1, ...
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BOOST_PP_ENUM_PARAMS(BOOST_PARAMETER_MAX_ARITY, class A)
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>
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arg_list( // A0& a0, A1& a1, ...
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BOOST_PP_ENUM_BINARY_PARAMS(BOOST_PARAMETER_MAX_ARITY, A, & a)
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)
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: Next( // a1, a2, ...
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BOOST_PP_ENUM_SHIFTED_PARAMS(BOOST_PARAMETER_MAX_ARITY, a)
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, void_reference()
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)
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, arg(a0)
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{}
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// Create a new list by prepending arg to a copy of tail. Used
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// when incrementally building this structure with the comma
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// operator.
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arg_list(TaggedArg head, Next const& tail)
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: Next(tail)
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, arg(head)
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{}
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// A metafunction class that, given a keyword and a default
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// type, returns the appropriate result type for a keyword
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// lookup given that default
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struct binding
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{
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template <class KW, class Default, class Reference>
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struct apply
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{
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typedef typename mpl::eval_if<
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boost::is_same<KW, key_type>
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, mpl::if_<Reference, reference, value_type>
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, mpl::apply_wrap3<typename Next::binding, KW, Default, Reference>
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>::type type;
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};
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};
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#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
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// Overload for key_type, so the assert below will fire if the
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// same keyword is used again
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static yes_tag has_key(key_type*);
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using Next::has_key;
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BOOST_MPL_ASSERT_MSG(
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sizeof(Next::has_key((key_type*)0)) == sizeof(no_tag)
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, duplicate_keyword, (key_type)
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);
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#endif
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//
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// Begin implementation of indexing operators for looking up
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// specific arguments by name
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//
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// Helpers that handle the case when TaggedArg is
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// empty<T>.
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template <class D>
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reference get_default(D const&, mpl::false_) const
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{
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return arg.value;
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}
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template <class D>
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reference get_default(D const& d, mpl::true_) const
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{
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return arg.value ? arg.value.get() : arg.value.construct(d.value);
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}
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#if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
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// These older compilers don't support the overload set creation
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// idiom well, so we need to do all the return type calculation
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// for the compiler and dispatch through an outer function template
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// A metafunction class that, given a keyword, returns the base
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// sublist whose get() function can produce the value for that
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// key.
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struct key_owner
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{
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template<class KW>
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struct apply
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{
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typedef typename mpl::eval_if<
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boost::is_same<KW, key_type>
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, mpl::identity<arg_list<TaggedArg,Next> >
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, mpl::apply_wrap1<typename Next::key_owner,KW>
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>::type type;
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};
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};
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// Outer indexing operators that dispatch to the right node's
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// get() function.
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template <class KW>
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typename mpl::apply_wrap3<binding, KW, void_, mpl::true_>::type
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operator[](keyword<KW> const& x) const
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{
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typename mpl::apply_wrap1<key_owner, KW>::type const& sublist = *this;
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return sublist.get(x);
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}
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template <class KW, class Default>
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typename mpl::apply_wrap3<binding, KW, Default&, mpl::true_>::type
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operator[](default_<KW, Default> x) const
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{
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typename mpl::apply_wrap1<key_owner, KW>::type const& sublist = *this;
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return sublist.get(x);
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}
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template <class KW, class F>
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typename mpl::apply_wrap3<
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binding,KW
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, typename result_of0<F>::type
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, mpl::true_
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>::type
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operator[](lazy_default<KW,F> x) const
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{
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typename mpl::apply_wrap1<key_owner, KW>::type const& sublist = *this;
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return sublist.get(x);
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}
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// These just return the stored value; when empty_arg_list is
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// reached, indicating no matching argument was passed, the
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// default is returned, or if no default_ or lazy_default was
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// passed, compilation fails.
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reference get(keyword<key_type> const&) const
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{
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BOOST_MPL_ASSERT_NOT((holds_maybe));
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return arg.value;
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}
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template <class Default>
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reference get(default_<key_type,Default> const& d) const
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{
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return get_default(d, holds_maybe());
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}
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template <class Default>
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reference get(lazy_default<key_type, Default>) const
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{
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return arg.value;
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}
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#else
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reference operator[](keyword<key_type> const&) const
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{
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BOOST_MPL_ASSERT_NOT((holds_maybe));
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return arg.value;
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}
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template <class Default>
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reference operator[](default_<key_type, Default> const& d) const
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{
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return get_default(d, holds_maybe());
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}
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template <class Default>
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reference operator[](lazy_default<key_type, Default>) const
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{
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return arg.value;
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}
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// Builds an overload set including operator[]s defined in base
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// classes.
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using Next::operator[];
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//
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// End of indexing support
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//
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//
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// For parameter_requirements matching this node's key_type,
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// return a bool constant wrapper indicating whether the
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// requirements are satisfied by TaggedArg. Used only for
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// compile-time computation and never really called, so a
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// declaration is enough.
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//
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template <class HasDefault, class Predicate, class ArgPack>
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static typename mpl::apply_wrap2<
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typename mpl::lambda<Predicate, lambda_tag>::type
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, value_type, ArgPack
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>::type
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satisfies(
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parameter_requirements<key_type,Predicate,HasDefault>*
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, ArgPack*
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);
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// Builds an overload set including satisfies functions defined
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// in base classes.
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using Next::satisfies;
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#endif
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// Comma operator to compose argument list without using parameters<>.
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// Useful for argument lists with undetermined length.
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template <class KW, class T2>
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arg_list<tagged_argument<KW, T2>, self>
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operator,(tagged_argument<KW,T2> x) const
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{
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return arg_list<tagged_argument<KW,T2>, self>(x, *this);
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}
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// MPL sequence support
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typedef self type; // Convenience for users
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typedef Next tail_type; // For the benefit of iterators
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typedef arg_list_tag tag; // For dispatching to sequence intrinsics
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};
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// MPL sequence support
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template <class ArgumentPack>
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struct arg_list_iterator
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{
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typedef mpl::forward_iterator_tag category;
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// The incremented iterator
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typedef arg_list_iterator<typename ArgumentPack::tail_type> next;
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// dereferencing yields the key type
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typedef typename ArgumentPack::key_type type;
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};
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template <>
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struct arg_list_iterator<empty_arg_list> {};
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}} // namespace parameter::aux
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// MPL sequence support
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namespace mpl
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{
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template <>
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struct begin_impl<parameter::aux::arg_list_tag>
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{
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template <class S>
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struct apply
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{
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typedef parameter::aux::arg_list_iterator<S> type;
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};
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};
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template <>
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struct end_impl<parameter::aux::arg_list_tag>
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{
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template <class>
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struct apply
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{
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typedef parameter::aux::arg_list_iterator<parameter::aux::empty_arg_list> type;
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};
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};
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}
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} // namespace boost
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#endif // ARG_LIST_050329_HPP
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