4 ms·

This is interesting... As non-C++ developer, I've never thought I needed this. Is this an answer to a question anyone is asking?

wyldfire 7y ago
Yes, your favorite high level language might provide something like this implicitly.
maxlybbert 7y ago
Perl has had this for decades. C’s strcmp() has similar semantics. I thought the motivation was that sort can be more efficient when each comparison can return more information (the standard library already has a sort function that relies only on using less-than operations). But people eventually realized that certain operations have to be implemented together to make sense. For instance, the sort function that relies only on less-than operations defines two values as equal if neither value is less than the other. Many people consider this weird, and wonder why sort doesn’t require both less-than and equality operations. The spaceship operator essentially implements a group of operations, and guarantees they’ll be consistent: less-than, equal, and greater-than (plus not-equal, less-than-or-equal, and greater-than-or-equal). Personally, I’m not thrilled about a special purpose solution to a single example of a problem (use this one operator to implement this group of related operations), but I do see some value in making it easy to implement this group of related operations.
ksherlock 7y ago
Yes. Aside from reducing repetitive code (replacing 7 overloaded comparison operators) it's probably more efficient. std::map, for example, currently uses a less-than comparator to order items, requiring multiple comparisons to check if items are equal.
mehrdadn 7y ago
The part you probably needed is 3-way comparisons. The weak vs. strong vs. distinction is less likely to be needed IMO.
de_watcher 7y ago
C++ just has this under-the-hood access to be able to define any comparison operator to do arbitrary things. C++20 is now more aware that this things are used for comparison, and it helps to make definitions shorter. Still handles non-totally-ordered cases fine.
iainmerrick 7y ago
As someone who has written comparison functions in C++ (probably incorrectly), yes, this would have been a godsend. Similarly, recent-ish innovations like std::move and std::unique_ptr may look complicated at first, but they genuinely made life a lot easier.

wyldfire 7y ago

Yes, your favorite high level language might provide something like this implicitly.

maxlybbert 7y ago

Perl has had this for decades. C’s strcmp() has similar semantics. I thought the motivation was that sort can be more efficient when each comparison can return more information (the standard library already has a sort function that relies only on using less-than operations). But people eventually realized that certain operations have to be implemented together to make sense. For instance, the sort function that relies only on less-than operations defines two values as equal if neither value is less than the other. Many people consider this weird, and wonder why sort doesn’t require both less-than and equality operations. The spaceship operator essentially implements a group of operations, and guarantees they’ll be consistent: less-than, equal, and greater-than (plus not-equal, less-than-or-equal, and greater-than-or-equal). Personally, I’m not thrilled about a special purpose solution to a single example of a problem (use this one operator to implement this group of related operations), but I do see some value in making it easy to implement this group of related operations.

ksherlock 7y ago

Yes. Aside from reducing repetitive code (replacing 7 overloaded comparison operators) it's probably more efficient. std::map, for example, currently uses a less-than comparator to order items, requiring multiple comparisons to check if items are equal.

mehrdadn 7y ago

The part you probably needed is 3-way comparisons. The weak vs. strong vs. distinction is less likely to be needed IMO.

de_watcher 7y ago

C++ just has this under-the-hood access to be able to define any comparison operator to do arbitrary things. C++20 is now more aware that this things are used for comparison, and it helps to make definitions shorter. Still handles non-totally-ordered cases fine.

iainmerrick 7y ago

As someone who has written comparison functions in C++ (probably incorrectly), yes, this would have been a godsend. Similarly, recent-ish innovations like std::move and std::unique_ptr may look complicated at first, but they genuinely made life a lot easier.