iter_swap() versus swap() — what’s the difference?

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The standard itself has very few mentions of iter_swap:

  • It should have the effect of swap(*a, *b), although there is no stipulation that it must be implemented that way.
  • The dereferenced values *a and *b must be “swappable”, which implies that swap(*a, *b) must be valid, and thus the dereferenced types must be identical, although the iterator types do not have to be.
  • iter_swap is required to be used in the implementation of std::reverse. No such requirement is placed on any other algorithm, so this seems to be an oddity.

To borrow what sehe had found from the SGI docs:

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).

All of these seem to suggest that it is an artifact of the past.

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