Re: [boost] [Signal] Variadic template implementation of signal/slot

Subject: Re: [boost] [Signal] Variadic template implementation of signal/slot
From: Frank Mori Hess (frank.hess_at_[hidden])
Date: 2009-05-28 15:47:17

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I've checked a variadic signal implementation into Boost.Signals2 on the svn 
trunk.  It is used when boost detects variadic template support.  The code 
still looks like macro hell, due to the continuing support for the 
non-variadic template implementation, but there is a noticeable improvement 
in compilation time.  The little hello_world_slot.cpp example program 
compiled about 10%-15% faster with gcc 4.3 for example.  However, the 
variadic Boost.Signals2 implementation still uses Boost.Function for its 
default SlotFunction and uses Boost.Bind, neither of which provide variadic 
templates implementations.  Out of curiosity I tested replacing them locally 
with the variadic std::function and std::bind in gcc 4.3, and that also 
produced an additional reduction in compile time.

I haven't updated the documentation yet, but the user-visible changes when 
using the variadic template implementation are as follows:  
1) The "portable syntax" classes like signal0, signal1, etc are gone. 
2) The member typedefs like "arg1_type", "arg2_type", etc are gone.  They are 
replaced with a "arg" member template class, so instead 
of "sig_type::arg1_type" you would do "sig_type::arg<0>::type".  For 
consistency the "arg" member template has also been added to the non-variadic 
implementation.

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