Allow custom types defined by static references #418
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generic over reference lifetime
aborgna-q
reviewed
Aug 17, 2023
src/utils.rs
Outdated
| @@ -39,3 +39,51 @@ pub(crate) mod test { | |||
| webbrowser::open(&base).unwrap(); | |||
| } | |||
| } | |||
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Leave the #[cfg(test)] block at the bottom.
src/extension/prelude.rs
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| SmolStr::new_inline("qubit"), | ||
| SmolStr::new_inline("prelude"), | ||
| TypeBound::Any, | ||
| ); | ||
|
|
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| pub(crate) const QB_T: Type = Type::new_extension(QB_CUSTOM_T); | ||
| pub(crate) const USIZE_T: Type = Type::new_extension(USIZE_CUSTOM_T); | ||
| pub(crate) const USIZE_CUSTOM_REF: &CustomType = &USIZE_CUSTOM_T; |
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Why do we need the explicit const references?
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I think because it is not temporary?
Checking quantinuum-hugr v0.1.0 (/Users/seyon/ng/hugr)
error[E0493]: destructor of `CustomType` cannot be evaluated at compile-time
--> src/extension/prelude.rs:66:59
|
66 | pub(crate) const QB_T: Type = Type::new_static_extension(&QB_CUSTOM_T);
| ^^^^^^^^^^^- value is dropped here
| |
| the destructor for this type cannot be evaluated in constants
error[E0716]: temporary value dropped while borrowed
--> src/extension/prelude.rs:66:59
|
66 | pub(crate) const QB_T: Type = Type::new_static_extension(&QB_CUSTOM_T);
| ----------------------------^^^^^^^^^^^-
| | | |
| | | temporary value is freed at the end of this statement
| | creates a temporary value which is freed while still in use
| argument requires that borrow lasts for `'static`
Some errors have detailed explanations: E0493, E0716.
For more information about an error, try `rustc --explain E0493`.
error: could not compile `quantinuum-hugr` (lib) due to 2 previous errors
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You'd need to use static instead of const so they are included in the compiled binary... But then you can't use it for the KnownTypeConst::TYPE const >.<
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Yeah I feel the static route is too painful - for now I've just made the reference constants private
src/utils.rs
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| fn eq(&self, other: &Self) -> bool { | ||
| match (self, other) { | ||
| // pointer equality can give false-negative | ||
| (Self::Static(l0), Self::Static(r0)) => std::ptr::eq(*l0, *r0) || l0 == r0, |
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This is only valid for T: Eq, otherwise you don't have reflexivity.
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Most of the time can avoid string comparison using pointer equality short circuiting.
Might be a bit sketch.