make TakeCell::empty() const, and make nrf52840 GPIO pin initialization a const fn #3937
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because of lifetimes the initialization cannot (yet) happen in a const
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This trick has actually worked for a long time (apparently, since 1.32 https://godbolt.org/z/5bWhYf5fP), but only because the const is defined as an associated constant. The mutable reference in a const error is triggered when you put the const elsewhere (e.g. in the body of |
brghena
previously approved these changes
Mar 27, 2024
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Bringing to the attention of @lschuermann |
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hudson-ayers
approved these changes
Mar 29, 2024
lschuermann
approved these changes
Apr 7, 2024
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Sorry for my late response; this looks good to me. I was pretty sure that this would still allow creation of trait objects due to this associated const not being part of the trait, but wanted to double check. This still works, so we won't run into any issues in the future here!
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Pull Request Overview
This pull request makes the
TakeCell::newfunction const. This requires an associated constant: moving the constant intofn newdoes not work, not using an explicit constant also does not work.That function being const can then be used to initialize the gpio pins for the ntrf52840 in a
const fn. It can't happen in an actual const because the final type contains a (non-static) lifetime.There are many more functions that can now become a
const fn: I can add some to this PR but those are scattered all around the codebase.Documentation Updated
/docs, or no updates are required.Formatting
make prepush.