StackOverflow2013

Note that there are some explanatory texts on larger screens.

plurals

PO
text
Body
copied!<p><strong>swap, when used by STL algorithms, is a free function</strong>. There is a default swap implementation: <code>std::swap</code>. It does the obvious. You seem to be under the impression that if you add a swap member function to your data type, STL containers and algorithms will find it and use it. This isn't the case.</p> <p>You're supposed to specialize std::swap (in the namespace next to your UDT, so it's found by ADL) if you can do better. It is idiomatic to just have it defer to a member swap function.</p> <p>While we're on the subject, it is also idiomatic in C++0x (in as much as is possible to have idioms on such a new standard) to implement rvalue constructors as a swap.</p> <p>And yes, in a world where a member swap was the language design instead of a free function swap, this would imply that we'd need a swap operator instead of a function - or else primitive types (int, float, etc) couldn't be treated generically (as they have no member function swap). So why didn't they do this? You'd have to ask the committee members for sure - but I'm 95% certain the reason is the committee has long preferred library implementions of features whenever possible, over inventing new syntax to implement a feature. The syntax of a swap operator would be weird, because unlike =, +, -, etc, and all the other operators, there is no algebraic operator everyone is familiar with for "swap".</p> <p>C++ is syntactically complex enough. They go to great lengths to not add new keywords or syntax features whenever possible, and only do so for very good reasons (lambdas!).</p>

Querying!

Guidance

An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload