universal reference for predicate in std::find_if()?

Asked Mar 25 '19 at 21:08

Active Mar 25 '19 at 22:52

Viewed 240 times

std::find_if's UnaryPredicate is by value. Why cannot we have it by universal reference? i.e.

template< class InputIt, class UnaryPredicate >
InputIt find_if( InputIt first, InputIt last, 
                 UnaryPredicate&& p );

Is it mostly for historical reasons, or is there reason to prefer pass by value over universal reference in this case even with c++11?

edited Mar 25 '19 at 22:52

Jarod42

asked Mar 25 '19 at 21:08

bill

3

Well, the interior of the algorithm is allowed to make copies so taking by reference could be misleading. – NathanOliver Mar 25 '19 at 21:14
And changing that might break old code, so I would say historical reasons. – Jarod42 Mar 25 '19 at 22:54

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