275 lines
9.8 KiB
C++
275 lines
9.8 KiB
C++
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/*=============================================================================
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Adaptable closures
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Phoenix V0.9
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Copyright (c) 2001-2002 Joel de Guzman
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Distributed under the Boost Software License, Version 1.0. (See
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accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt)
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URL: http://spirit.sourceforge.net/
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==============================================================================*/
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#ifndef PHOENIX_CLOSURES_HPP
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#define PHOENIX_CLOSURES_HPP
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///////////////////////////////////////////////////////////////////////////////
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#include "boost/lambda/core.hpp"
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///////////////////////////////////////////////////////////////////////////////
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namespace boost {
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namespace lambda {
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///////////////////////////////////////////////////////////////////////////////
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//
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// Adaptable closures
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//
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// The framework will not be complete without some form of closures
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// support. Closures encapsulate a stack frame where local
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// variables are created upon entering a function and destructed
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// upon exiting. Closures provide an environment for local
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// variables to reside. Closures can hold heterogeneous types.
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//
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// Phoenix closures are true hardware stack based closures. At the
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// very least, closures enable true reentrancy in lambda functions.
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// A closure provides access to a function stack frame where local
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// variables reside. Modeled after Pascal nested stack frames,
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// closures can be nested just like nested functions where code in
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// inner closures may access local variables from in-scope outer
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// closures (accessing inner scopes from outer scopes is an error
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// and will cause a run-time assertion failure).
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//
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// There are three (3) interacting classes:
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//
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// 1) closure:
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//
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// At the point of declaration, a closure does not yet create a
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// stack frame nor instantiate any variables. A closure declaration
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// declares the types and names[note] of the local variables. The
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// closure class is meant to be subclassed. It is the
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// responsibility of a closure subclass to supply the names for
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// each of the local variable in the closure. Example:
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//
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// struct my_closure : closure<int, string, double> {
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//
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// member1 num; // names the 1st (int) local variable
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// member2 message; // names the 2nd (string) local variable
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// member3 real; // names the 3rd (double) local variable
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// };
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//
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// my_closure clos;
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//
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// Now that we have a closure 'clos', its local variables can be
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// accessed lazily using the dot notation. Each qualified local
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// variable can be used just like any primitive actor (see
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// primitives.hpp). Examples:
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//
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// clos.num = 30
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// clos.message = arg1
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// clos.real = clos.num * 1e6
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//
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// The examples above are lazily evaluated. As usual, these
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// expressions return composite actors that will be evaluated
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// through a second function call invocation (see operators.hpp).
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// Each of the members (clos.xxx) is an actor. As such, applying
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// the operator() will reveal its identity:
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//
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// clos.num() // will return the current value of clos.num
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//
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// *** [note] Acknowledgement: Juan Carlos Arevalo-Baeza (JCAB)
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// introduced and initilally implemented the closure member names
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// that uses the dot notation.
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//
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// 2) closure_member
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//
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// The named local variables of closure 'clos' above are actually
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// closure members. The closure_member class is an actor and
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// conforms to its conceptual interface. member1..memberN are
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// predefined typedefs that correspond to each of the listed types
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// in the closure template parameters.
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//
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// 3) closure_frame
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//
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// When a closure member is finally evaluated, it should refer to
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// an actual instance of the variable in the hardware stack.
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// Without doing so, the process is not complete and the evaluated
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// member will result to an assertion failure. Remember that the
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// closure is just a declaration. The local variables that a
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// closure refers to must still be instantiated.
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//
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// The closure_frame class does the actual instantiation of the
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// local variables and links these variables with the closure and
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// all its members. There can be multiple instances of
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// closure_frames typically situated in the stack inside a
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// function. Each closure_frame instance initiates a stack frame
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// with a new set of closure local variables. Example:
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//
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// void foo()
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// {
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// closure_frame<my_closure> frame(clos);
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// /* do something */
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// }
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//
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// where 'clos' is an instance of our closure 'my_closure' above.
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// Take note that the usage above precludes locally declared
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// classes. If my_closure is a locally declared type, we can still
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// use its self_type as a paramater to closure_frame:
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//
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// closure_frame<my_closure::self_type> frame(clos);
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//
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// Upon instantiation, the closure_frame links the local variables
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// to the closure. The previous link to another closure_frame
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// instance created before is saved. Upon destruction, the
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// closure_frame unlinks itself from the closure and relinks the
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// preceding closure_frame prior to this instance.
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//
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// The local variables in the closure 'clos' above is default
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// constructed in the stack inside function 'foo'. Once 'foo' is
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// exited, all of these local variables are destructed. In some
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// cases, default construction is not desirable and we need to
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// initialize the local closure variables with some values. This
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// can be done by passing in the initializers in a compatible
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// tuple. A compatible tuple is one with the same number of
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// elements as the destination and where each element from the
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// destination can be constructed from each corresponding element
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// in the source. Example:
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//
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// tuple<int, char const*, int> init(123, "Hello", 1000);
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// closure_frame<my_closure> frame(clos, init);
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//
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// Here now, our closure_frame's variables are initialized with
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// int: 123, char const*: "Hello" and int: 1000.
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//
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///////////////////////////////////////////////////////////////////////////////
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///////////////////////////////////////////////////////////////////////////////
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//
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// closure_frame class
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//
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///////////////////////////////////////////////////////////////////////////////
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template <typename ClosureT>
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class closure_frame : public ClosureT::tuple_t {
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public:
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closure_frame(ClosureT& clos)
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: ClosureT::tuple_t(), save(clos.frame), frame(clos.frame)
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{ clos.frame = this; }
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template <typename TupleT>
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closure_frame(ClosureT& clos, TupleT const& init)
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: ClosureT::tuple_t(init), save(clos.frame), frame(clos.frame)
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{ clos.frame = this; }
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~closure_frame()
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{ frame = save; }
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private:
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closure_frame(closure_frame const&); // no copy
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closure_frame& operator=(closure_frame const&); // no assign
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closure_frame* save;
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closure_frame*& frame;
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};
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///////////////////////////////////////////////////////////////////////////////
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//
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// closure_member class
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//
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///////////////////////////////////////////////////////////////////////////////
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template <int N, typename ClosureT>
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class closure_member {
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public:
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typedef typename ClosureT::tuple_t tuple_t;
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closure_member()
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: frame(ClosureT::closure_frame_ref()) {}
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template <typename TupleT>
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struct sig {
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typedef typename detail::tuple_element_as_reference<
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N, typename ClosureT::tuple_t
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>::type type;
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};
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template <class Ret, class A, class B, class C>
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// typename detail::tuple_element_as_reference
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// <N, typename ClosureT::tuple_t>::type
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Ret
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call(A&, B&, C&) const
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{
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assert(frame);
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return boost::tuples::get<N>(*frame);
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}
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private:
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typename ClosureT::closure_frame_t*& frame;
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};
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///////////////////////////////////////////////////////////////////////////////
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//
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// closure class
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//
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///////////////////////////////////////////////////////////////////////////////
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template <
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typename T0 = null_type,
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typename T1 = null_type,
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typename T2 = null_type,
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typename T3 = null_type,
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typename T4 = null_type
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>
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class closure {
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public:
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typedef tuple<T0, T1, T2, T3, T4> tuple_t;
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typedef closure<T0, T1, T2, T3, T4> self_t;
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typedef closure_frame<self_t> closure_frame_t;
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closure()
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: frame(0) { closure_frame_ref(&frame); }
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closure_frame_t& context() { assert(frame); return frame; }
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closure_frame_t const& context() const { assert(frame); return frame; }
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typedef lambda_functor<closure_member<0, self_t> > member1;
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typedef lambda_functor<closure_member<1, self_t> > member2;
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typedef lambda_functor<closure_member<2, self_t> > member3;
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typedef lambda_functor<closure_member<3, self_t> > member4;
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typedef lambda_functor<closure_member<4, self_t> > member5;
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private:
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closure(closure const&); // no copy
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closure& operator=(closure const&); // no assign
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template <int N, typename ClosureT>
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friend class closure_member;
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template <typename ClosureT>
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friend class closure_frame;
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static closure_frame_t*&
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closure_frame_ref(closure_frame_t** frame_ = 0)
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{
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static closure_frame_t** frame = 0;
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if (frame_ != 0)
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frame = frame_;
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return *frame;
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}
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closure_frame_t* frame;
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};
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}}
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// namespace
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#endif
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