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Subject: Re: [boost] Call for interest - BOOST_AUTO_FUNCTION
From: Yechezkel Mett (ymett.on.boost_at_[hidden])
Date: 2010-10-10 08:02:34

On Tue, Oct 5, 2010 at 9:20 PM, Matt Calabrese <rivorus_at_[hidden]> wrote:
> I've been noticing that a lot of times in 0x code I've found it useful to
> create a very simple "auto function" macro that uses trailing return type
> syntax with decltype with 1-liner functions that automatically repeats the
> same expression in both the return type and the return statement.
> #define AUTO_FUN( name, param_list, expression )
>  \
> auto name param_list -> decltype( expression ) { return expression; }

Why not simply

auto name = [&](param_list){ return expression; }


> There are two big advantages to this. The first and most obvious one is that
> it reduces redundancy when you have a 1-line function template which has a
> difficult to deduce return type that you generally would use decltype on,
> and the more subtle benefit is that since the exact expression is repeated
> in the return type you automatically get "perfect-fit" SFINAE. By that I
> mean it provides a quick way to SFINAE-out potential instantiations before
> instantiating the implementation. Because of this, even though a return type
> may be simple to deduce without decltype, the macro is still a valuable tool
> since it can cause substitution to fail if the body of a function template
> would fail to instantiate. You get very basic, automatic, syntax-only
> concept checking for free. It's a simple macro, but I find that it gets lots
> of use.

I don't know if my suggestion would give sfinae, though.

Yechezkel Mett

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