[boost] Re: python 'in' syntax mini-lib RFC

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2004-05-19 13:00:52

Max Khesin wrote:
> I have been playing around with a library to emulate Python 'in' syntax
> 
> if(a in [x1, x2]):
> 	stuff
> 
> the main motivation for this is the annoyance of repeating the || operator
> with the same value in C++
> 
> if(val==v1 || val==v2 || val==v3){
>   ^^^           ^^^           ^^^
> }
> 
> I figured I would use tuple for the list to allow membership test for a list
> of heterogeneous types (just like python).
> The rough results are included below.
> 
> I am interested in your feedback:
> 1) how useful would you find this in general

Different types don't seem useful to me, otherwise it might be a handy 
tool from time to time.

> 2) there are 3 variations on syntax in the main() 1st is native(no macros)
> with more typing, 2 is less typing with macros, 3d is even less but does not
> compile :) (coule use a language lawer here). Do you like any of these?
> Alternative suggestions?

find( e ).in( v1, v2, v3, v4 );

Does seem more natural to me for a C++-program. I don't see why we 
should limit our thinking to a Python-like syntax.

One thing to keep in mind: The ||-form has short-circuiting. While it 
might look convenient to have a nicer syntax, we should also think about 
what drawbacks it has if applied blindly by users, e.g. more errors, 
inefficiency. Maybe we should even consider a macro-only solution like:

BOOST_CONTAINED( e )( v1 )( v2 )( v3 );

or something...

Regards, Daniel

-- 
Daniel Frey
aixigo AG - financial solutions & technology
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eMail: daniel.frey_at_[hidden], web: http://www.aixigo.de