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Re: Why doesn't iter_swap use swap?

Hello self :)

Just to pad out my earlier mail, it looks like intel's implementation does use swap to implement iter_swap, and stlport's implementation requires the two parameters to iter_swap must have the same type (unlike the standard).

There is also a defect report against iter_swap ( , defect 187 ), which discusses how to be honest it's a bit of a mess.

I see this has been previously posted about but wasn't discussed in depth. However for performing STL algorithms in constructs of any kind of complexity I imagine this is causing some serious dents in performance.

One reason discussed in the standard about why not to use swap() is that iter_swap may work in some places where swap() doesn't (vector<bool> is mentioned). I'm not an expert on this, but we seem to in general require "normal assignment" in for example __unguarded_linear_insert, and other places.

I'm happy to continue investigating this, but I suspect someone else might be able to advise quickly what is going on. If it turns out that we can't or won't change iter_swap in general, then a large number of overloads may have to be defined as at the moment many algorithms are not using swap and are therefore much more expensive than they should be.


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