Actually, the compiler can distinguish between sort(Range, Pred) and sort(Iter, Iter). This is a C++98 feature, partial ordering of function templates. Basically, if you call sort(range, pred) then the sort(Iter, Iter) overload will be ignored (since template argument deduction can't succeed - Iter can't be two different types). If you call sort(iter1, iter2) then both overloads are viable, but sort(Iter, Iter) is preferred - partial ordering determines that it matches a strictly smaller infinite universe of types.

This is also why C++14's dual-range algorithms didn't lead to ambiguities: equal(InIt1, InIt1, InIt2, Pred) versus equal(InIt1, InIt1, InIt2, InIt2) has the same structure.

(Obviously if you have a type that is both a range and a predicate, then it's ambiguous.)