STLAlgorithmExtensions/ForEachIf

(Note that this implementation is dependent upon the result of the Defect Report submitted by Anthony Williams regarding whether it is legal to dereference an input iterator multiple times. If the resulting clarification indicates that input iterators shall only be dereferenced once, this algorithm will need to be revised in a manner similar to the more elaborate version of CopyIf)

The committee have responded to the defect report to say "there is no basis for the assumption that an InputIterator? cannot be dereferenced twice", so the following implementation should be correct.

 //Performs f() on any element elem in [first, last) where pred(elem) is true
 template<typename InputIterator, typename Predicate, typename UnaryFunction>
 UnaryFunction for_each_if(InputIterator first, InputIterator last, 
                           Predicate pred, UnaryFunction f)
 {
     for(;first != last; ++first)
     {
         if (pred(*first))
         {
             f(*first);
         }
     }
     return f;
 }