Begin documenting initialization checking #2174
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this is not particularly pretty, but I believe it complies with the union RFC and it doesn't appear to create much conflict.
text/2094-nll.md
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| - supporting prefixes were defined earlier | ||
| - so: reading a path like `a` is illegal if `a.b` is mutably | ||
| borrowed, but -- in contrast with shallow accesses -- reading `a` is also | ||
| illegal if `*a` is mutably borrowed | ||
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| And the accessed data and all children in its lvalue tree must be definitely initialized. |
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Is this sentence fragment supposed to be connected to the "3." bullet point immediately above, or something higher up?
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cc @pnkfelix |
| ```Rust | ||
| let x: (u32, u32); | ||
| x.0 = 4; | ||
| x.1 = 5; |
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In the current borrow checker, we do not accept this program. Are there corner cases that I am overlooking here?
Presuming there are not, I think that the current borrow checker basically enforces a rule like "Assigning to an lvalue LV requires that all prefixes of LV are definitely initialized", right?
Maybe we should just adopt this rule for now?
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This is indeed a difference from the current borrow checker. I see no problem with this rule.
Centril
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I think I'd like to move these changes over to /~https://github.com/nikomatsakis/nll-rfc/ -- I still view that as the 'official home' of the NLL RFC, at least until stabilization. |
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@nikomatsakis What do you want to do with this RFC? |
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I'm going to try to follow @nikomatsakis 's request and turn this PR into a PR against /~https://github.com/nikomatsakis/nll-rfc/ ; after I have created that second PR, I will close this one. |
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Okay as promised (too long ago) I have trivially ported ariel's hard work over to nikomatsakis/nll-rfc#51 I did not attempt to fill in any of the todo's in the text; that can happen over on the nll-rfc repo. Closing as any future work should happen over there. |
If we're going to have a spec for the borrow checker, it shouldn't leave out important components.
Edit: Rendered