BOOST OVERLOAD (updated 2007/10/28)

================================================================= Copyright (c) 2007 Marco Cecchetti

Use, modification and distribution of this library 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)

================================================================= WARNING this library is a proof of concept implementation only, and it comes without ABSOLUTELY ANY WARRANTY !

WARNING: at present Boost Overload IS NOT a Boost library !

================================================================= Please report any bugs, compiler issues, comment or suggestion to [email protected]

Library Description

Boost Overload behaves as an overloaded Boost Function. Actually it wraps multiple Boost Function objects of different signatures.

Library Documentation

http://docs.google.com/View?docid=dhd386mp_16gxsfxn

Library Tutorial

http://docs.google.com/Doc?id=dfxvjncs_1x6456m

• version 0.3.0 (overload-0.3.0.zip) *

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tested with boost version: 1.33.1, 1.34.1

Compiler support table

compiler OS test

gcc 4.1.2 under Linux pass intel 9.1 under Linux pass mingw 3.4.2 under Windows pass mingw 3.2.3 under Windows fail MS VC++ 8.0 under Windows pass MS VC++ 7.1 under Windows partial*

*all test passed but signature deduction of multi-signature function objects you have to use the signature based syntax with them.

what's new

• added partial support for MSVC 7.1, all work but signature deduction of multi-signature function objects, you have to use the signature based syntax in order to set multi-signature function objects as callable targets;

• you can set a free function overload or a member function overload as callable target through the signature based syntax for more info give a look to the new paragraph in the tuturial; the same applies to template free functions and template member functions;

• added two new helper methods

  • the empty_all method that tell us if all callable targets are empty;
  • the clear_all method that clears all the callable targets;

• in the folder libs/overload/example you can find all the examples presented in the tutorial;

• fixed some minor issue.

• version 0.2.2 (overload-0.2.2.zip) *

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tested with boost version: 1.33.1, 1.34.1

Compiler support table

compiler OS test

gcc 4.1.2 under Linux pass intel 9.1 under Linux pass mingw 3.4.2 under Windows pass mingw 3.2.3 under Windows fail MS VC++ 8.0 under Windows pass MS VC++ 7.1 under Windows fail

description

I went on working on the second implementation only. The source code has gone through refactoring and modularization. The signature deduction policy used by the "set" method is changed in the part concerned with multi-signature function objects. This is a complete and detailed description of the signature deduction policy:

Let be "ov" an instantiation of the template class overload for a given set of signatures "ss" used as template arguments:

• if the new candidate callable target "f" is a free function or a member function then:
  • if "f" is not overloaded and its signature is included in "ss" then the new target (i.e. "f") replaces the target tied to the matching signature;
  • if the signature of "f" is not included in "ss" a compile time error is produced;
  • if "f" is overloaded an "unresolved overloaded function type" compile time error is produced; (we can't rely on the Mesonides' trick, or equivalent for free functions, because they require to know the function name in advance); this is the same behaviour followed by boost.function; note: when I say that a function member signature is included in "ss" I actually mean that a const or non-const explicit signature of the given member function is included in "ss";
• if the new candidate callable target "f" is a function object (possibly a multi-signature one ) then:
  • let be "rs" the set of signatures that are defined by its overload resolution set (or it would be better to say "by the overload resolution set of f::operator()" ); note that for a function object with a template operator() "rs" is an infinite set;
  • if the intersection between "rs" and "ss" is empty the assignment fails and a compile time error is produced;
  • if the intersection between "rs" and "ss" is not empty then the new target (i.e. "f") replaces all the targets related to the signatures included in the intersection.

• version 0.1 (overload-0.1.zip) *

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tested on gcc 4.1.2 under Linux

description

The archive includes two implementations.

• in the first implementation, I deduce function object signature by exploiting template function argument deduction; if the signature is not discovered no error is reported, and error handling is demanded to boost::function at call time; signature deduction of multi-signature function objects cause an "unresolved overloaded function type" compile error;

• in the second implementation, if the signature is not deduced a compile time error is produced; signature deduction of multi-signature function objects is successfull if it exists one and only one signature registered in the overload that matches with the function object, else an ad-hoc compile time error, pointing out the ambiguity, is produced.