source: downloads/boost_1_34_1/libs/spirit/phoenix/example/fundamental/sample9.cpp @ 29

/*=============================================================================
    Phoenix V1.2.1
    Copyright (c) 2001-2003 Joel de Guzman

    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)
==============================================================================*/
#include <vector>
#include <algorithm>
#include <iostream>

#define PHOENIX_LIMIT 5
#include <boost/spirit/phoenix/operators.hpp>
#include <boost/spirit/phoenix/primitives.hpp>
#include <boost/spirit/phoenix/composite.hpp>
#include <boost/spirit/phoenix/special_ops.hpp>
#include <boost/spirit/phoenix/statements.hpp>

namespace phoenix {

///////////////////////////////////////////////////////////////////////////////
//
//  local_tuple
//
//      This *is a* tuple like the one we see in TupleT in any actor
//      base class' eval member function. local_tuple should look and
//      feel the same as a tupled-args, that's why it is derived from
//      TupleArgsT. It has an added member, locs which is another tuple
//      where the local variables will be stored. locs is mutable to
//      allow read-write access to our locals regardless of
//      local_tuple's constness (The eval member function accepts it as
//      a const argument).
//
///////////////////////////////////////////////////////////////////////////////
template <typename TupleArgsT, typename TupleLocsT>
struct local_tuple : public TupleArgsT {

    typedef TupleLocsT local_vars_t;
    typedef TupleArgsT parent_t;

    local_tuple(TupleArgsT const& args, TupleLocsT const& locs_)
    :   TupleArgsT(args), locs(locs_) {}

    TupleArgsT&         parent()        { return *this; }
    TupleArgsT const&   parent() const  { return *this; }

    mutable TupleLocsT locs;
};

///////////////////////////////////////////////////////////////////////////////
//
//  local_var_result
//
//      This is a return type computer. Given a constant integer N, a
//      parent index and a tuple, get the Nth local variable type. The
//      parent index is an integer specifying which parent scope to
//      access; 0==current scope, 1==parent scope, 2==parent's parent
//      scope.
//
//      This is a metaprogram with partial specializations. There is a
//      general case, a special case for local_tuples and a terminating
//      special case for local_tuples.
//
//      General case: If TupleT is not really a local_tuple, we just return nil_t.
//
//      local_tuples case:
//          Parent index is 0: We get the Nth local variable.
//          Otherwise: We subclass from local_tuples<N, Parent-1, TupleArgsT>
//
///////////////////////////////////////////////////////////////////////////////
template <int N, int Parent, typename TupleT>
struct local_var_result {

    typedef nil_t type;
};

//////////////////////////////////
template <int N, int Parent, typename TupleArgsT, typename TupleLocsT>
struct local_var_result<N, Parent, local_tuple<TupleArgsT, TupleLocsT> >
:   public local_var_result<N, Parent-1, TupleArgsT> {};

//////////////////////////////////
template <int N, typename TupleArgsT, typename TupleLocsT>
struct local_var_result<N, 0, local_tuple<TupleArgsT, TupleLocsT> > {

    typedef typename tuple_element<
        N, TupleLocsT
    >::type& type;

    static type get(local_tuple<TupleArgsT, TupleLocsT> const& tuple)
    { return tuple.locs[tuple_index<N>()]; }
};

///////////////////////////////////////////////////////////////////////////////
//
//  local_var
//
//      This class looks so curiously like the argument class. local_var
//      provides access to the Nth local variable packed in the tuple
//      duo local_tuple above. Parent specifies the Nth parent scope.
//      0==current scope, 1==parent scope, 2==parent's parent scope. The
//      member function parent<N>() may be called to provide access to
//      outer scopes.
//
//      Note that the member function eval expects a local_tuple
//      argument. Otherwise there will be acompile-time error. local_var
//      primitives only work within the context of a context_composite
//      (see below).
//
//      Provided are some predefined local_var actors for 0..N local
//      variable access: loc1..locN.
//
///////////////////////////////////////////////////////////////////////////////
template <int N, int Parent = 0>
struct local_var {

    template <typename TupleT>
    struct result {

        typedef typename local_var_result<N, Parent, TupleT>::type type;
    };

    template <typename TupleT>
    typename local_var_result<N, Parent, TupleT>::type
    eval(TupleT const& tuple) const
    {
        return local_var_result<N, Parent, TupleT>::get(tuple);
    }

    template <int PIndex>
    actor<local_var<N, Parent+PIndex> >
    parent() const
    {
        return local_var<N, Parent+PIndex>();
    }
};

//////////////////////////////////
namespace locals {

    actor<local_var<0> > const result   = local_var<0>();
    actor<local_var<1> > const loc1     = local_var<1>();
    actor<local_var<2> > const loc2     = local_var<2>();
    actor<local_var<3> > const loc3     = local_var<3>();
    actor<local_var<4> > const loc4     = local_var<4>();
}

///////////////////////////////////////////////////////////////////////////////
//
//  context_composite
//
//      This class encapsulates an actor and some local variable
//      initializers packed in a tuple.
//
//      context_composite is just like a proxy and delegates the actual
//      evaluation to the actor. The actor does the actual work. In the
//      eval member function, before invoking the embedded actor's eval
//      member function, we first stuff an instance of our locals and
//      bundle both 'args' and 'locals' in a local_tuple. This
//      local_tuple instance is created in the stack initializing it
//      with our locals member. We then pass this local_tuple instance
//      as an argument to the actor's eval member function.
//
///////////////////////////////////////////////////////////////////////////////
template <typename ActorT, typename LocsT>
struct context_composite {

    typedef context_composite<ActorT, LocsT> self_t;

    template <typename TupleT>
    struct result { typedef typename tuple_element<0, LocsT>::type type; };

    context_composite(ActorT const& actor_, LocsT const& locals_)
    :   actor(actor_), locals(locals_) {}

    template <typename TupleT>
    typename tuple_element<0, LocsT>::type
    eval(TupleT const& args) const
    {
        local_tuple<TupleT, LocsT>  local_context(args, locals);
        actor.eval(local_context);
        return local_context.locs[tuple_index<0>()];
    }

    ActorT actor;
    LocsT locals;
};

///////////////////////////////////////////////////////////////////////////////
//
//  context_gen
//
//      At construction time, this class is given some local var-
//      initializers packed in a tuple. We just store this for later.
//      The operator[] of this class creates the actual context_composite
//      given an actor. This is responsible for the construct
//      context<types>[actor].
//
///////////////////////////////////////////////////////////////////////////////
template <typename LocsT>
struct context_gen {

    context_gen(LocsT const& locals_)
    :   locals(locals_) {}

    template <typename ActorT>
    actor<context_composite<typename as_actor<ActorT>::type, LocsT> >
    operator[](ActorT const& actor)
    {
        return context_composite<typename as_actor<ActorT>::type, LocsT>
            (as_actor<ActorT>::convert(actor), locals);
    }

    LocsT locals;
};

///////////////////////////////////////////////////////////////////////////////
//
//    Front end generator functions. These generators are overloaded for
//    1..N local variables. context<T0,... TN>(i0,...iN) generate context_gen
//    objects (see above).
//
///////////////////////////////////////////////////////////////////////////////
template <typename T0>
inline context_gen<tuple<T0> >
context()
{
    typedef tuple<T0> tuple_t;
    return context_gen<tuple_t>(tuple_t(T0()));
}

//////////////////////////////////
template <typename T0, typename T1>
inline context_gen<tuple<T0, T1> >
context(
    T1 const& _1 = T1()
)
{
    typedef tuple<T0, T1> tuple_t;
    return context_gen<tuple_t>(tuple_t(T0(), _1));
}

//////////////////////////////////
template <typename T0, typename T1, typename T2>
inline context_gen<tuple<T0, T1, T2> >
context(
    T1 const& _1 = T1(),
    T2 const& _2 = T2()
)
{
    typedef tuple<T0, T1, T2> tuple_t;
    return context_gen<tuple_t>(tuple_t(T0(), _1, _2));
}

//////////////////////////////////
template <typename T0, typename T1, typename T2, typename T3>
inline context_gen<tuple<T0, T1, T2, T3> >
context(
    T1 const& _1 = T1(),
    T2 const& _2 = T2(),
    T3 const& _3 = T3()
)
{
    typedef tuple<T0, T1, T2, T3> tuple_t;
    return context_gen<tuple_t>(tuple_t(T0(), _1, _2, _3));
}

//////////////////////////////////
template <typename T0, typename T1, typename T2, typename T3, typename T4>
inline context_gen<tuple<T0, T1, T2, T3, T4> >
context(
    T1 const& _1 = T1(),
    T2 const& _2 = T2(),
    T3 const& _3 = T3(),
    T4 const& _4 = T4()
)
{
    typedef tuple<T0, T1, T2, T3> tuple_t;
    return context_gen<tuple_t>(tuple_t(T0(), _1, _2, _3, _4));
}

///////////////////////////////////////////////////////////////////////////////
}

//////////////////////////////////
using namespace std;
using namespace phoenix;
using namespace phoenix::locals;

//////////////////////////////////
int
main()
{
    context<nil_t>(1)
    [
        cout << loc1 << '\n',
        context<nil_t>(2)
        [
            cout << loc1.parent<1>() << ' ' << loc1 << '\n',
            context<nil_t>(3)
            [
                cout << loc1.parent<2>() << ' ' << loc1.parent<1>() << ' ' << loc1 << '\n'
            ]
        ]
    ]

    ();

    return 0;
}