/*============================================================================= | |
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 class 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 |