std::swap vs std::exchange swap(x, y) and exchange(x, y) are not the same thing. exchange(x, y) never assigns a new value to y. You could do so if you use it like this: y = exchange(x, y). But that isn’t the main use case for exchange(x, y). N3668 includes the statement: The benefit isn’t huge, but … Read more
No. This is not acceptable. This code invokes Undefined behavior. This is because of the operation on b is not defined. In the expression a=(a+b)-(b=a); it is not certain whether b gets modified first or its value gets used in the expression (a+b) because of the lack of the sequence point. See what standard syas: … Read more
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 … Read more
Am I wrong? Nope, you’re absolutely right – as is your example timeline. In addition to it not being atomic, it’s not guaranteed that the write to id will be picked up by the other thread anyway, given that there’s no synchronization and the field isn’t volatile. It’s somewhat disconcerting for reference material like this … Read more
Nope. You could have a function to make it more concise each place you use it, but in the end, the work done would be the same (plus the overhead of the function call, until/unless HotSpot moved it inline — to help it with that, make the function static final).
EDIT: Okay, got it. The first point to make is that obviously you shouldn’t use this code anyway. However, when you expand it, it becomes equivalent to: j = j ^ (i = i ^ (j = j ^ i)); (If we were using a more complicated expression such as foo.bar++ ^= i, it would … Read more
How is std::swap implemented? Yes, the implementation presented in the question is the classic C++03 one. A more modern (C++11) implementation of std::swap looks like this: template<typename T> void swap(T& t1, T& t2) { T temp = std::move(t1); // or T temp(std::move(t1)); t1 = std::move(t2); t2 = std::move(temp); } This is an improvement over the … Read more
I think what you are looking for is iter_swap which you can find also in <algorithm>. all you need to do is just pass two iterators each pointing at one of the elements you want to exchange. since you have the position of the two elements, you can do something like this: // assuming your … Read more
What you want is a very expensive operation in an ArrayList. It requires shifting every element between the beginning of the list and the location of C down by one. However, if you really want to do it: int index = url.indexOf(itemToMove); url.remove(index); url.add(0, itemToMove); If this is a frequent operation for you, and random … Read more
TL;DR There isn’t a built-in function. Use swap3() as mentioned below. Summary As many mentioned, there are multiple ways to do this, most noticable are these 4 methods: function swap1(&$x, &$y) { // Warning: works correctly with numbers ONLY! $x ^= $y ^= $x ^= $y; } function swap2(&$x, &$y) { list($x,$y) = array($y, $x); … Read more