/*=============================================================================
Adaptable closures
Phoenix V0.9
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)
URL: http://spirit.sourceforge.net/
==============================================================================*/
#ifndef PHOENIX_CLOSURES_HPP
#define PHOENIX_CLOSURES_HPP
///////////////////////////////////////////////////////////////////////////////
#include "boost/lambda/core.hpp"
///////////////////////////////////////////////////////////////////////////////
namespace boost {
namespace lambda {
///////////////////////////////////////////////////////////////////////////////
//
// Adaptable closures
//
// The framework will not be complete without some form of closures
// support. Closures encapsulate a stack frame where local
// variables are created upon entering a function and destructed
// upon exiting. Closures provide an environment for local
// variables to reside. Closures can hold heterogeneous types.
//
// Phoenix closures are true hardware stack based closures. At the
// very least, closures enable true reentrancy in lambda functions.
// A closure provides access to a function stack frame where local
// variables reside. Modeled after Pascal nested stack frames,
// closures can be nested just like nested functions where code in
// inner closures may access local variables from in-scope outer
// closures (accessing inner scopes from outer scopes is an error
// and will cause a run-time assertion failure).
//
// There are three (3) interacting classes:
//
// 1) closure:
//
// At the point of declaration, a closure does not yet create a
// stack frame nor instantiate any variables. A closure declaration
// declares the types and names[note] of the local variables. The
// closure class is meant to be subclassed. It is the
// responsibility of a closure subclass to supply the names for
// each of the local variable in the closure. Example:
//
// struct my_closure : closure<int, string, double> {
//
// member1 num; // names the 1st (int) local variable
// member2 message; // names the 2nd (string) local variable
// member3 real; // names the 3rd (double) local variable
// };
//
// my_closure clos;
//
// Now that we have a closure 'clos', its local variables can be
// accessed lazily using the dot notation. Each qualified local
// variable can be used just like any primitive actor (see
// primitives.hpp). Examples:
//
// clos.num = 30
// clos.message = arg1
// clos.real = clos.num * 1e6
//
// The examples above are lazily evaluated. As usual, these
// expressions return composite actors that will be evaluated
// through a second function call invocation (see operators.hpp).
// Each of the members (clos.xxx) is an actor. As such, applying
// the operator() will reveal its identity:
//
// clos.num() // will return the current value of clos.num
//
// *** [note] Acknowledgement: Juan Carlos Arevalo-Baeza (JCAB)
// introduced and initilally implemented the closure member names
// that uses the dot notation.
//
// 2) closure_member
//
// The named local variables of closure 'clos' above are actually
// closure members. The closure_member class is an actor and
// conforms to its conceptual interface. member1..memberN are
// predefined typedefs that correspond to each of the listed types
// in the closure template parameters.
//
// 3) closure_frame
//
// When a closure member is finally evaluated, it should refer to
// an actual instance of the variable in the hardware stack.
// Without doing so, the process is not complete and the evaluated
// member will result to an assertion failure. Remember that the
// closure is just a declaration. The local variables that a
// closure refers to must still be instantiated.
//
// The closure_frame class does the actual instantiation of the
// local variables and links these variables with the closure and
// all its members. There can be multiple instances of
// closure_frames typically situated in the stack inside a
// function. Each closure_frame instance initiates a stack frame
// with a new set of closure local variables. Example:
//
// void foo()
// {
// closure_frame<my_closure> frame(clos);
// /* do something */
// }
//
// where 'clos' is an instance of our closure 'my_closure' above.
// Take note that the usage above precludes locally declared
// classes. If my_closure is a locally declared type, we can still
// use its self_type as a paramater to closure_frame:
//
// closure_frame<my_closure::self_type> frame(clos);
//
// Upon instantiation, the closure_frame links the local variables
// to the closure. The previous link to another closure_frame
// instance created before is saved. Upon destruction, the
// closure_frame unlinks itself from the closure and relinks the
// preceding closure_frame prior to this instance.
//
// The local variables in the closure 'clos' above is default
// constructed in the stack inside function 'foo'. Once 'foo' is
// exited, all of these local variables are destructed. In some
// cases, default construction is not desirable and we need to
// initialize the local closure variables with some values. This
// can be done by passing in the initializers in a compatible
// tuple. A compatible tuple is one with the same number of
// elements as the destination and where each element from the
// destination can be constructed from each corresponding element
// in the source. Example:
//
// tuple<int, char const*, int> init(123, "Hello", 1000);
// closure_frame<my_closure> frame(clos, init);
//
// Here now, our closure_frame's variables are initialized with
// int: 123, char const*: "Hello" and int: 1000.
//
///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
//
// closure_frame class
//
///////////////////////////////////////////////////////////////////////////////
template <typename ClosureT>
class closure_frame : public ClosureT::tuple_t {
public:
closure_frame(ClosureT& clos)
: ClosureT::tuple_t(), save(clos.frame), frame(clos.frame)
{ clos.frame = this; }
template <typename TupleT>
closure_frame(ClosureT& clos, TupleT const& init)
: ClosureT::tuple_t(init), save(clos.frame), frame(clos.frame)
{ clos.frame = this; }
~closure_frame()
{ frame = save; }
private:
closure_frame(closure_frame const&); // no copy
closure_frame& operator=(closure_frame const&); // no assign
closure_frame* save;
closure_frame*& frame;
};
///////////////////////////////////////////////////////////////////////////////
//
// closure_member class
//
///////////////////////////////////////////////////////////////////////////////
template <int N, typename ClosureT>
class closure_member {
public:
typedef typename ClosureT::tuple_t tuple_t;
closure_member()
: frame(ClosureT::closure_frame_ref()) {}
template <typename TupleT>
struct sig {
typedef typename detail::tuple_element_as_reference<
N, typename ClosureT::tuple_t
>::type type;
};
template <class Ret, class A, class B, class C>
// typename detail::tuple_element_as_reference
// <N, typename ClosureT::tuple_t>::type
Ret
call(A&, B&, C&) const
{
assert(frame);
return boost::tuples::get<N>(*frame);
}
private:
typename ClosureT::closure_frame_t*& frame;
};
///////////////////////////////////////////////////////////////////////////////
//
// closure class
//
///////////////////////////////////////////////////////////////////////////////
template <
typename T0 = null_type,
typename T1 = null_type,
typename T2 = null_type,
typename T3 = null_type,
typename T4 = null_type
>
class closure {
public:
typedef tuple<T0, T1, T2, T3, T4> tuple_t;
typedef closure<T0, T1, T2, T3, T4> self_t;
typedef closure_frame<self_t> closure_frame_t;
closure()
: frame(0) { closure_frame_ref(&frame); }
closure_frame_t& context() { assert(frame); return frame; }
closure_frame_t const& context() const { assert(frame); return frame; }
typedef lambda_functor<closure_member<0, self_t> > member1;
typedef lambda_functor<closure_member<1, self_t> > member2;
typedef lambda_functor<closure_member<2, self_t> > member3;
typedef lambda_functor<closure_member<3, self_t> > member4;
typedef lambda_functor<closure_member<4, self_t> > member5;
private:
closure(closure const&); // no copy
closure& operator=(closure const&); // no assign
template <int N, typename ClosureT>
friend struct closure_member;
template <typename ClosureT>
friend class closure_frame;
static closure_frame_t*&
closure_frame_ref(closure_frame_t** frame_ = 0)
{
static closure_frame_t** frame = 0;
if (frame_ != 0)
frame = frame_;
return *frame;
}
closure_frame_t* frame;
};
}}
// namespace
#endif