neon: Relax the lifetime constraints on TypedArray borrows
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kjvalencik
commented
Mar 22, 2022
| /// This may not be used if a mutable borrow is in scope. For the dynamically | ||
| /// checked variant see [`TypedArray::try_borrow`]. | ||
| fn as_slice<'a: 'b, 'b, C>(&'b self, cx: &'b C) -> &'b [Self::Item] | ||
| fn as_slice<'cx, 'a, C>(&self, cx: &'a C) -> &'a [Self::Item] |
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'a is renamed to 'cx across the board for clarity. 'b becomes 'a since that's the only lifetime we need.
kjvalencik
commented
Mar 22, 2022
| /// This may not be used if any other borrow is in scope. For the dynamically | ||
| /// checked variant see [`TypedArray::try_borrow_mut`]. | ||
| fn as_mut_slice<'a: 'b, 'b, C>(&'b mut self, cx: &'b mut C) -> &'b mut [Self::Item] | ||
| fn as_mut_slice<'cx, 'a, C>(&mut self, cx: &'a mut C) -> &'a mut [Self::Item] |
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The 'a: 'b bound was unnecessarily complicated. It's not possible to have references that don't meet this requirement.
kjvalencik
commented
Mar 22, 2022
| &self, | ||
| lock: &'b Lock<'b, C>, | ||
| ) -> Result<Ref<'b, Self::Item>, BorrowError> | ||
| fn try_borrow<'cx, 'a, C>(&self, lock: &'a Lock<C>) -> Result<Ref<'a, Self::Item>, BorrowError> |
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Elided the inner lifetime of Lock to simplify.
kjvalencik
commented
Mar 22, 2022
| } | ||
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| if let Ok(v) = v.downcast::<JsBuffer, _>(cx) { | ||
| return Ok(Cow::Borrowed(v.as_slice(cx))); |
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This is the primary thing we are trying to allow; returning a reference to a handle that was downcast.
dherman
approved these changes
Mar 23, 2022
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dherman
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dherman
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I feel like I should have some suggestion, but borrowck did all the heavy lifting for me :P
LGTM!
| } | ||
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| if let Ok(v) = v.downcast::<JsBuffer, _>(cx) { | ||
| return Ok(Cow::Borrowed(v.as_slice(cx))); |
The current lifetimes are overly restrictive. The reference is valid for as long as the handle is valid. Since the `Context` is always the most narrow scope, it will be valid for at *least* as long as `Context`, even if the `Handle` type is dropped. This allows downcasting and returning a borrow within the same function.
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The current lifetimes are overly restrictive. The reference is valid for as long as the handle is valid. Since the
Contextis always the most narrow scope, it will be valid for at least as long asContext, even if theHandletype is dropped. This allows downcasting and returning a borrow within the same function.See this thread for more details. https://rust-bindings.slack.com/archives/C0HE1SA65/p1647378845225649