[MIR] Change destination accessor to return references #30761
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nagisa
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☔ The latest upstream changes (presumably #30757) made this pull request unmergeable. Please resolve the merge conflicts. |
| @@ -425,7 +425,7 @@ pub trait MutVisitor<'tcx> { | |||
| } | |||
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| Terminator::Call { ref mut func, ref mut args, ref mut kind } => { | |||
| if let Some(ref mut destination) = kind.destination() { | |||
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indeed, this was definitely a bug.
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r+ but I suspect this conflicted with @michaelwoerister's macroization of the visitor |
Previously it was returning a value, mostly for the two reasons: * Cloning Lvalue is very cheap most of the time (i.e. when Lvalue is not a Projection); * There’s users who want &mut lvalue and there’s users who want &lvalue. Returning a value allows to make either one easier when pattern matching (i.e. Some(ref dest) or Some(ref mut dest)). However, I’m now convinced this is an invalid approach. Namely the users which want a mutable reference may modify the Lvalue in-place, but the changes won’t be reflected in the final MIR, since the Lvalue modified is merely a clone. Instead, we have two accessors `destination` and `destination_mut` which return a reference to the destination in desired mode.
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Before #30757 this actually caused a bug in the |
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@bors r+ |
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📌 Commit 2f86c16 has been approved by |
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…elwoerister Previously it was returning a clone, mostly for the two reasons: * Cloning Lvalue is very cheap most of the time (i.e. when Lvalue is not a Projection); * There’s users who want &mut lvalue and there’s users who want &lvalue. Returning a value allows to make either one easier when pattern matching (i.e. Some(ref dest) or Some(ref mut dest)). However, I’m now convinced this is an invalid approach. Namely the users which want a mutable reference may modify the Lvalue in-place, but the changes won’t be reflected in the final MIR, since the Lvalue modified is merely a clone. Instead, we have two accessors `destination` and `destination_mut` which return a reference to the destination in desired mode. r? @nikomatsakis
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Previously it was returning a clone, mostly for the two reasons: * Cloning Lvalue is very cheap most of the time (i.e. when Lvalue is not a Projection); * There’s users who want &mut lvalue and there’s users who want &lvalue. Returning a value allows to make either one easier when pattern matching (i.e. Some(ref dest) or Some(ref mut dest)). However, I’m now convinced this is an invalid approach. Namely the users which want a mutable reference may modify the Lvalue in-place, but the changes won’t be reflected in the final MIR, since the Lvalue modified is merely a clone. Instead, we have two accessors `destination` and `destination_mut` which return a reference to the destination in desired mode. r? @nikomatsakis
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@bors: retry force |
nagisa
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…elwoerister Previously it was returning a clone, mostly for the two reasons: * Cloning Lvalue is very cheap most of the time (i.e. when Lvalue is not a Projection); * There’s users who want &mut lvalue and there’s users who want &lvalue. Returning a value allows to make either one easier when pattern matching (i.e. Some(ref dest) or Some(ref mut dest)). However, I’m now convinced this is an invalid approach. Namely the users which want a mutable reference may modify the Lvalue in-place, but the changes won’t be reflected in the final MIR, since the Lvalue modified is merely a clone. Instead, we have two accessors `destination` and `destination_mut` which return a reference to the destination in desired mode. r? @nikomatsakis
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Previously it was returning a clone, mostly for the two reasons:
to make either one easier when pattern matching (i.e. Some(ref dest) or Some(ref mut dest)).
However, I’m now convinced this is an invalid approach. Namely the users which want a mutable
reference may modify the Lvalue in-place, but the changes won’t be reflected in the final MIR,
since the Lvalue modified is merely a clone.
Instead, we have two accessors
destinationanddestination_mutwhich return a reference to thedestination in desired mode.
r? @nikomatsakis