Re: [boost] Giving names to formal parameters of lambda expressions: a named placeholder trick.

From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2008-03-31 10:29:23

On Sun, Mar 30, 2008 at 11:18 PM, shunsuke <pstade.mb_at_[hidden]> wrote:
> Giovanni Piero Deretta wrote:
>  > OTOH,  refactoring a lambda on a separate function object is a pain if
>  > you have to figure out the result of a complex composition
>  > of polymorphic function objects (result_of helps only to a point). For
>  > example, what is the result of:
>  >
>  > filter_view(reverse_view(mapped_view(range, op)), filter)
>  >
>  > (I often find much more complex expressions in my code).
>
>  BTW, how about this:
>  http://tinyurl.com/23jdk6
>  return_of is a simple wrapper around result_of.

Ah, yes, basically recursive evaluation of result_of. I have it in my
bag of tools (and as an added benefit, is boost::lambda, compatible,
but I guess return_of is too); it still bothers me to have to write an
expression two times, one to deduce the result_type and one to
actually compute the value. And it seems that things won't improve
much with decltype [1].

This is in fact the reason for my compose<> template idea: If you
can't avoid writing a type expression, you might as well just write
that.

[1] it would be great if we also had the automatic one-line-lambda
result type deduction in normal functions (and polymorphic lambdas
too, but that's another story :( ).
-- 
gpd