any swaps inefficiently

[jonathandodd@…]

Apologies if this isn't a bug - I am quite new to boost, however I checked in the IRC channel and it doesn't seem like this is a total non-starter.

It seems that if you simply call swap, std::swap is called, resulting in an inefficient swapping operation. For example:

Big b1, b2; any a1=b1, a2=b2;

swap(a1,a2); Calls std::swap, invokes three copy constructors

I've attached a demonstration file, which I compiled with gcc.

Seems like can be easily solved with an overloaded std::swap, but I know little about boost, so I'll leave that for the experts :)

[jonathandodd@…]

demo of any::swap

[Bryce Adelstein Lelbach]

As I explained on IRC, this is not inefficient. Two copy ctor calls happen in the construction of the boost::any objects.

[jonathandodd@…]

To clarify, when I run this there are in fact 5 copy constructor calls, 3 of which were generated by swap.

I have been assured that this is just me not turning on compiler optimisations, or not using boost::swap. However, even with the -o3 switch in gcc, and even with boost::swap, I still get 3 copy constructor calls. Since the best thing to do is just to swap over the pointers, I expected none.