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