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///////////////////////////////////////////////////////////////////////////////
// lambda.hpp
//
// Copyright 2008 Eric Niebler. 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)
#include <sstream>
#include <boost/mpl/int.hpp>
#include <boost/mpl/min_max.hpp>
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/mpl/next_prior.hpp>
#include <boost/fusion/tuple.hpp>
#include <boost/typeof/typeof.hpp>
#include <boost/typeof/std/sstream.hpp>
#include <boost/typeof/std/ostream.hpp>
#include <boost/typeof/std/iostream.hpp>
#include <boost/type_traits/add_const.hpp>
#include <boost/type_traits/add_reference.hpp>
#include <boost/proto/core.hpp>
#include <boost/proto/context.hpp>
#include <boost/proto/transform.hpp>
#include <boost/test/unit_test.hpp>
#include <boost/test/floating_point_comparison.hpp>
using namespace boost;
// Forward declaration of the lambda expression wrapper
template<typename T>
struct lambda;
struct lambda_domain
: proto::domain<proto::pod_generator<lambda> >
{};
template<typename I>
struct placeholder
{
typedef I arity;
};
template<typename T>
struct placeholder_arity
{
typedef typename T::arity type;
};
namespace grammar
{
using namespace proto;
// The lambda grammar, with the transforms for calculating the max arity
struct Lambda
: or_<
when< terminal< placeholder<_> >, mpl::next<placeholder_arity<_value> >() >
, when< terminal<_>, mpl::int_<0>() >
, when< nary_expr<_, vararg<_> >, fold<_, mpl::int_<0>(), mpl::max<Lambda,_state>()> >
>
{};
}
// simple wrapper for calculating a lambda expression's arity.
template<typename Expr>
struct lambda_arity
: boost::result_of<grammar::Lambda(Expr, mpl::void_, mpl::void_)>
{};
// The lambda context is the same as the default context
// with the addition of special handling for lambda placeholders
template<typename Tuple>
struct lambda_context
: proto::callable_context<lambda_context<Tuple> const>
{
lambda_context(Tuple const &args)
: args_(args)
{}
template<typename Sig>
struct result;
template<typename This, typename I>
struct result<This(proto::tag::terminal, placeholder<I> const &)>
: fusion::result_of::at<Tuple, I>
{};
template<typename I>
typename fusion::result_of::at<Tuple, I>::type
operator ()(proto::tag::terminal, placeholder<I> const &) const
{
return fusion::at<I>(this->args_);
}
Tuple args_;
};
// The lambda<> expression wrapper makes expressions polymorphic
// function objects
template<typename T>
struct lambda
{
BOOST_PROTO_BASIC_EXTENDS(T, lambda<T>, lambda_domain)
BOOST_PROTO_EXTENDS_ASSIGN()
BOOST_PROTO_EXTENDS_SUBSCRIPT()
// Careful not to evaluate the return type of the nullary function
// unless we have a nullary lambda!
typedef typename mpl::eval_if<
typename lambda_arity<T>::type
, mpl::identity<void>
, proto::result_of::eval<T const, lambda_context<fusion::tuple<> > >
>::type nullary_type;
// Define our operator () that evaluates the lambda expression.
nullary_type operator ()() const
{
fusion::tuple<> args;
lambda_context<fusion::tuple<> > ctx(args);
return proto::eval(*this, ctx);
}
#define M0(N, typename_A, A_const_ref, A_const_ref_a, ref_a) \
template<typename_A(N)> \
typename proto::result_of::eval<T const, lambda_context<fusion::tuple<A_const_ref(N)> > >::type \
operator ()(A_const_ref_a(N)) const \
{ \
fusion::tuple<A_const_ref(N)> args(ref_a(N)); \
lambda_context<fusion::tuple<A_const_ref(N)> > ctx(args); \
return proto::eval(*this, ctx); \
} \
/**/
BOOST_PROTO_REPEAT_FROM_TO(1, 4, M0)
#undef M0
};
// Define some lambda placeholders
lambda<proto::terminal<placeholder<mpl::int_<0> > >::type> const _1 = {{}};
lambda<proto::terminal<placeholder<mpl::int_<1> > >::type> const _2 = {{}};
lambda<proto::terminal<placeholder<mpl::int_<3> > >::type> const _3 = {{}};
template<typename T>
lambda<typename proto::terminal<T>::type> const val(T const &t)
{
lambda<typename proto::terminal<T>::type> that = {{t}};
return that;
}
template<typename T>
lambda<typename proto::terminal<T &>::type> const var(T &t)
{
lambda<typename proto::terminal<T &>::type> that = {{t}};
return that;
}
void test_lambda()
{
BOOST_CHECK_EQUAL(11, ( (_1 + 2) / 4 )(42));
BOOST_CHECK_EQUAL(-11, ( (-(_1 + 2)) / 4 )(42));
BOOST_CHECK_CLOSE(2.58, ( (4 - _2) * 3 )(42, 3.14), 0.1);
// check non-const ref terminals
std::stringstream sout;
(sout << _1 << " -- " << _2)(42, "Life, the Universe and Everything!");
BOOST_CHECK_EQUAL("42 -- Life, the Universe and Everything!", sout.str());
// check nullary lambdas
BOOST_CHECK_EQUAL(3, (val(1) + val(2))());
// check array indexing for kicks
int integers[5] = {0};
(var(integers)[2] = 2)();
(var(integers)[_1] = _1)(3);
BOOST_CHECK_EQUAL(2, integers[2]);
BOOST_CHECK_EQUAL(3, integers[3]);
}
using namespace unit_test;
///////////////////////////////////////////////////////////////////////////////
// init_unit_test_suite
//
test_suite* init_unit_test_suite( int argc, char* argv[] )
{
test_suite *test = BOOST_TEST_SUITE("test expression template domains");
test->add(BOOST_TEST_CASE(&test_lambda));
return test;
}
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