undefined | Better HN

0 pointscycloptic5y ago0 comments

Thank you for the examples. I'm not sure std::function is a good comparison. After some research it seems this used to be in the spec, but it was removed because nobody supported it correctly and it seems it was too difficult to do it in a type-safe manner anyway: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p030...

The other thing is that Zig doesn't seem to have any real plans to support C++-style closures right now. If they ever find a type-safe way to do it while supporting custom allocators, then that would be interesting, but at the moment I wouldn't say it's any better than C++ in this regard.

I actually have seen some C/C++ libraries that do allow changing the default allocator although it's usually only low-level libraries that bother to do this.

0 comments

3 comments · 1 top-level

int_19h5y ago· 2 in thread

C++-style closures are unrelated to custom allocators, since they're not heap-allocated.

mwkaufma5y ago

You are correct that the type the compiler creates for a lambda is allocated in-place, usually on the stack, and perform no heap-allocs. However if you pass it to a std:: function it will be _boxed_ and std::function _will_ heap alloc the space for it. This alloc is what's not customizable.

int_19h5y ago

That's fair, but std::function is not specifically about lambdas (As Boost.Function, it predates them, in fact) - it's about wrapping an arbitrary callable in a way that allows erasing its type. Idiomatic C++ rarely uses that class - I don't think it's used anywhere else in the standard library, even though it has plenty of higher-order functions etc. Turns out that closures that can only be passed in and not returned are still plenty useful.

1 more reply

j / k navigate · click thread line to collapse