C++ Weekly - Ep 436 - Transforming Lambda Captures

[@fcolecumberri]

This is one of those features I love I can use and I hate the confusing way it is written.

[@czarsonxd2093]

had no clue about this

[@AndiAbrudan]

Wow, this is more useful than just the casting part. I find working with the expansion operator very cumbersome; maybe because I haven't studied all the rules. But with this syntax, you're moving the expansion at the top of the lambda, and you're free to use `strlike` as a single object inside the body. Awesome video!

[@AtomicAndi]

Thanks for pointing that out. The video was maybe not so awesome after all, because I missed the point about the expansion being kind of outside

[@majohime]

If only I could find more cool variadic templates/fold expressions related stuff like this

[@cppweekly]

Upcoming talk at CppCon 2024 will dig into some of this stuff.

This is madness!

[@BenjaminWheeler0510]

I am lost on all the ellipses unfortunately :( which videos do you cover those on again?

[@UsernameUsername0000]

Look up parameter pack and then fold expressions.

[@ohwow2074]

It's crazy. I have never heard of this particular use of parameter pack expansion. I guess it'll come in handy.

[@Rosen2221]

Literally wrote a subsystem for transporting some version information between client and server, which had almost the exact same function and problem as this video. The function in question was just merging single tokens (from constexpr defines, strings at hand in the version constructing class and other string_view like identifier). WIth the lambda capture we can output a total_size from the single tokens (of whatever stringlike type) and create a new string with reserved size onto which to append

[@N....]

Ahh ok, I see now what you were talking about, that is indeed simpler than the way I suggested, cool!

[@ihatelhp]

Surely there are reasons why the ... comes before the identifier initializer?

[@abhinavk0929]

...iden is the syntax to inroduce a parameter pack with the name "iden". So 'strlike' is a pack that consists of string_views into the parameter strings.

[@PedroOliveira-sl6nw]

What about lifetime of string views? In this simple case it's okay. But imagine that you return the lambda (instead of void function).

[@cppweekly]

Yes, that's a potential problem. kzbin.info/www/bejne/mYbZlaeCia-Ym8U

[@badassopenpolling]

nice!

[@SylphDS]

I feel like this is the kind of code you can only read for a about a week after you write it, and then if you read it again at any point after that you get instantly lost in the folding expressions. They are not very intuitive.

[@diablo384]

Does the string_view{...input} make another copy in that lambda function? I can't get it.

[@cppweekly]

string_view is never a copy, so it's just creating a view (pointer + length) for each string-like thing passed in. This is not 0 cost, necessarily, but it is very low cost. It might incur some strlen calls sometimes, but otherwise should just be copying 2 pointer-sized things per element.

[@troylowry4239]

Wtf is going on in the comments

[@majohime]

At least no bots spouting slurs, still kinda weird

[@RomanOrekhov]

probably the word "captures" triggered the bots

[@AtomicAndi]

Weird example. I'd rather have work_with_stringlike take everything by stringview. How would the code look then?

[@anon_y_mousse]

It's this kind of garbage syntax why I've been working on my own language and the issue with strings is why the default string type in my language *is* a string view.

[@sigasigasiga]

std::size be like "oh yeah why am i needed anyway"

[@N....]

The funny thing about slideware is its selective memory since it's trying to be relevant in other contexts too