I just read the code for std::for_each:
template<class InputIterator, class Function>
Function for_each(InputIterator first, InputIterator last, Function f)
{
for ( ; first!=last; ++first ) f(*first);
return f;
}
and could not see any good reasons for this template function to return the input function. Does anyone have any examples on where this would be useful?
It's to allow you to accrue state in your function and then return it to your calling code. For instance, your function (as a functor class) could have a member int for counting the number of times it had been called.
Here is a page with some examples : https://web.archive.org/web/20171127171924/http://xenon.arcticus.com/c-morsels-std-for-each-functors-member-variables
No particular reason I guess. What you can do though is using the returned function in another foreach call, thus avoiding writing the function name twice and possibly making a mistake there.