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From: "Deja User" <gennaro_prota@my-deja.com>
Newsgroups: comp.std.c++
Subject: Re: Proposal: change to condition ? value1 : value2
Date: Mon, 26 Feb 2001 23:07:14 GMT
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On Thu, 22 Feb 2001 23:32:53 GMT, gt5163b@prism.gatech.edu (Brian McNamara!) wrote:


>Does something like this suffice?
>
>   template <class T>
>   T ifElseDefault( T value, T def) {
>      return value ? value : def ;
>   }
>   
>   const char *comma = ifElseDefault( strchr(input, ','), "");
>
>It seems to me a function provides the same abstraction without any need
>to extend the language.  
>
>(Although, if the default value is an expression with side-effects that
>shouldn't be evaluated if the condition is true, then indeed, the
>function above is insufficient.  Indeed, I can't even find a solution
>with a macro.)
>

Hehe... :-)))  So it seems that the extension Greg Brewer proposes makes sense!

Just a note: it is natural, in my opinion, that:

  cond? : expr2;

should not evaluate cond twice, even if cond is true; this is different from

cond? cond : expr2,


For instance,

    const char* input = "This, has, commas";
    const char *comma = strchr(input, ',')?   :   "";

should cause at the most one call of strchr.

[I refer to the proposed extension for the ?: operator... i'm not saying that your function
template produces a double evaluation, it's obvious that one evaluation of the
argument used to initialize the parameter 'value' occurs :-)  ]

What do you think about it?

     Gennaro Prota

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