Std::ascii in core?

derekdreery · 2017-11-17T18:02:46.610Z

Is there a reason std::ascii isn’t in core - it doesn’t seem to rely on I/O or alloc?

To give some background: I’m writing a library for formatting byte arrays using std::ascii::escape_default, and there’s not any reason not to make it #[no_std], except for the fact that ascii isn’t in core.

cuviper · 2017-11-17T18:57:58.394Z

AsciiExt has methods using Self::Owned that allocate for str and [u8], but I suppose those implementation could be in the alloc crate while the trait is in core.

mbrubeck · 2017-11-17T18:59:22.828Z

Is liballoc allowed to impl AsciiExt for str if neither the trait nor str is defined by liballoc? (I know for normal crates the answer is no, but do the standard libraries have a way around this?)

cuviper · 2017-11-17T19:03:38.667Z

mbrubeck:

Is liballoc allowed to impl AsciiExt for str

Oh, right... but #[lang = "str"] impl str is in alloc already, so I think it might work.

derekdreery · 2017-11-17T19:10:53.537Z

cuviper:

AsciiExt has methods using Self::Owned that allocate for str and [u8], but I suppose those implementation could be in the alloc crate while the trait is in core.

Oh right - my use case uses escape_default so I didn't see those. It's more difficult than I thought.

cuviper:

Oh, right… but #[lang = "str"] impl str is in alloc already, so I think it might work.

It would be great if it did - you never know when you need to escape ascii on microcontrollers!

cuviper · 2017-11-17T19:27:24.817Z

It should also be possible to put escape_default and EscapeDefault in core, AsciiExt in alloc, then re-export them together in std::ascii.

derekdreery · 2017-11-17T19:32:23.757Z

cuviper:

It should also be possible to put escape_default and EscapeDefault in core, AsciiExt in alloc, then re-export them together in std::ascii.

This would solve my use case, but I feel some of the methods on AsciiExt are useful without alloc, for example to_upper on a u8. Maybe it isn't worth the hassle of including them in core though.

EDIT: or maybe it's simply not possible, because of impl rules.

sfackler · 2017-11-17T20:40:24.405Z

We’ve recently moved AsciiExt’s methods off of the trait and into the individual types as inherent impls.

derekdreery · 2017-11-18T13:32:49.242Z

sfackler:

We’ve recently moved AsciiExt’s methods off of the trait and into the individual types as inherent impls.

In that case, I'll just put an issue in to suggest the move for escape_default and EscapeDefault.

system · 2019-03-25T08:29:16.771Z

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