What's the point of iter_swap?

Question

I was just wondering, why would anybody write this:

std::iter_swap(i, k);

instead of this?

std::swap(*i, *k);   // saved a          


        

Answer 1

From the SGI docs (here):

[1] Strictly speaking, iter_swap is redundant. It exists only for technical reasons: in some circumstances, some compilers have difficulty performing the type deduction required to interpret swap(*a, *b).

Answer 2

To answer your second question, the using + swap allows the compiler to use user-defined swap functions that may be more efficient than the default implementation (by using ADL). Explicitly saying std::swap inhibits ADL and any custom swap methods it maybe have been able to find.

As for iter_swap it's presumably there to use in templates and clearly indicate intention rather than a swap that might indicate you expect a pointer.