Why does std::for_each(from, to, function) return function?

Question

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?

Accepted Answer

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

Why does std::for_each(from, to, function) return function?

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