Re: std::for_each + break
On Nov 20, 1:13 pm, Kai-Uwe Bux <jkherci...@gmx.net> wrote:
terminator wrote:
On Nov 20, 12:45 pm, Kai-Uwe Bux <jkherci...@gmx.net> wrote:
Kira Yamato wrote:
On 2007-11-19 07:12:29 -0500, yurec <Yurij.Zha...@materialise.kiev.ua=
said:
I wanna give template method of library class with some predicate,
which I put to std::for_each in that method.How to break the
std::for_each with predicate?(exceptions are used olny in exceptiona=
l
situations, as i know)
I would think throwing an exception is a simple and
elegant solution here.
Simple and elegant? in this case?
Compare
try {
std::for_each( seq.begin(), seq.end(), throwing_predicate_and_actio=
n
);
}
catch ( whatever ) {}
Anyone who wrote that at any place where I've ever worked would
not be allowed to touch the code again. Exceptions are NOT a
flow control mechanism.
[...]
what`s wrong with std::find_if when breaking is needed?
It depends: std::find_if conveys the intent of searching. It
goes against expectations to use it with a predicate whose
evaluation leaves side-effects on the container elements.
std::find_if definitly conveys the wrong message. In addition,
the standard is very explicit: "The function object pred shall
not apply any non-constant function through the dereferenced
iterator." That definitly limits the possible uses of find_if
here.
On the other hand, std::for_each carries no such connotation
(although some people feel otherwise on the ground that the
standard classifies it as non-mutating).
On the third hand: std::for_each very definitely conveys the
intent of visiting *every* element in the sequence, exactly
once.
Perhaps the real problem is just to redefine the sequence.
Boost has some very nice iterator adaptors, for example, and if
you have an std::vector, nothing says that you can't use some
special iterators which stop along the way.
So, std::find_if is not a good substitute for std::for_each in
the case where you just want a loop that performs some action
on an initial segment of the list.
I guess, the way to do this idiomatically in STLeese is
something like:
std::for_each( begin, std::find_if( begin, end, condition ),
action );
I'm not sure about "idiomatically in STLeese". The STL is
really very poorly designed for this sort of thing. Look at the
hoops the Boost iterator adapters have to jump through.
Still, some sort of iterator adapter would seem the logical
solution.
--
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