问题
I was just wondering, why would anybody write this:
std::iter_swap(i, k);
instead of this?
std::swap(*i, *k); // saved a few keystrokes!
Then I looked into the implementation of iter_swap, and of course it only uses swap instead of std::swap since we're already in namespace std, anyway. That leads me to the next question:
Why would anybody write this:
using std::swap;
swap(a, b);
instead of this?
std::iter_swap(&a, &b); // saved an entire line of code!
Are there any important differences/issues I am overlooking here?
回答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).
回答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.
来源：https://stackoverflow.com/questions/13991909/whats-the-point-of-iter-swap