How can I use operator [] ?

[Michael-Tieying-Zhang]

It seems there is no operator [] in current libcuckoo. But our code uses [] that is supported in the old version of libcuckoo. How can I keep my code unchanged if I use current version of libcuckoo?

[manugoyal]

Hey so we decided to deprecate that feature, since the semantics were kind of messy, not optimally performant in general, and encouraged non-threadsafe patterns. Most usages of operator[] should map directly to existing functions. For example, if operator[] is used as an rvalue, find should suffice. If used as an lvalue, upset should suffice. Refactoring this way may actually increase the performance of your code, too.

[Michael-Tieying-Zhang]

If used as an lvalue, upset should suffice.

I guess you mean upsert?

For example, I have a cuckoomaptbl<int, class* pointer>, and originally I did like this: tbl[5] = pointer;

Now I should do like this:

auto fn = [pointer](class *&p) {
   p = pointer;
};
tbl.upsert(id, fn, pointer);

It's too messy for the code.

[manugoyal]

Well I guess it really depends on what you're trying to do. If you are sure the key isn't already in the table, you can do an insert, or if you're sure the key already is in the table, you can do an update. Both of those are one liners.

I agree that upsert in the case you're trying to do is a bit clumsy. But the bracket operator syntax does basically the same thing, but in a less flexible and performant way than upset. Perhaps you could define a helper function that takes in a table reference, key, and value, and does the upset the way you want?

[Michael-Tieying-Zhang]

does the upset the way you want

Upset or upsert? There is no upset API, I guess.

[manugoyal]

Yeah sorry i think my phone keeps autocorrecting. It's upsert

[Michael-Tieying-Zhang]

Alright. I think you can close this issue for now. If I have questions, I will re-open it. Thanks!

[manugoyal]

Cool! Seems like C++17 has an insert_or_assign function in their API that may be worth emulating in libcuckoo.

[manugoyal]

Just added insert_or_assign in 8d247ab97b228565c08be16b763d8cb861d147b4. This should have the functionality you described.

[Michael-Tieying-Zhang]

@manugoyal Thanks!