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Remove cross-borrowing entirely #15349

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pcwalton opened this issue Jul 2, 2014 · 5 comments · Fixed by #16917
Closed

Remove cross-borrowing entirely #15349

pcwalton opened this issue Jul 2, 2014 · 5 comments · Fixed by #16917
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A-typesystem Area: The type system
Milestone
1.0

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@pcwalton
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pcwalton commented Jul 2, 2014

Tracking bug for RFC PR rust-lang/rfcs#139.

Nominating for 1.0, P-backcompat-lang.
@pcwalton pcwalton mentioned this issue Jul 2, 2014
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@lilyball
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lilyball commented Jul 2, 2014

This needs to be blocked on DST. @wycats pointed out in IRC that this breaks the ability to coerce Box<Trait> to &Trait. The expected solution is to use &*x, but that's not legal until DST lands.

@lilyball
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lilyball commented Jul 2, 2014

Summary of IRC discussion:

@pcwalton feels that transmute() is an acceptable solution. Others disagree. @nick29581 says that the part of DST that allows this is estimated to land in ~2 weeks. @pcwalton has agreed that ~2 weeks is an acceptable amount of time to delay this.

@pcwalton
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pcwalton commented Jul 2, 2014

Note that, per later discussion, this doesn't have to block cross-borrowing entirely, just cross-borrowing for traits.

@pnkfelix
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pnkfelix commented Jul 3, 2014

Assigning P-backcompat-lang, 1.0 milestone.

@pnkfelix pnkfelix added this to the 1.0 milestone Jul 3, 2014
@aturon aturon mentioned this issue Jul 4, 2014
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@pcwalton pcwalton mentioned this issue Jul 7, 2014
Merged
pcwalton added a commit to pcwalton/rust that referenced this issue Jul 17, 2014
@pcwalton
librustc: Remove cross-borrowing of Box<T> to &T from the language,
de70d76 
except where trait objects are involved.

Part of issue rust-lang#15349, though I'm leaving it open for trait objects.
Cross borrowing for trait objects remains because it is needed until we
have DST.

This will break code like:

    fn foo(x: &int) { ... }

    let a = box 3i;
    foo(a);

Change this code to:

    fn foo(x: &int) { ... }

    let a = box 3i;
    foo(&*a);

[breaking-change]
bors added a commit that referenced this issue Jul 17, 2014
@bors
auto merge of #15515 : pcwalton/rust/cross-borrowing, r=alexcrichton
e288fc6 
except where trait objects are involved.

Part of issue #15349, though I'm leaving it open for trait objects.
Cross borrowing for trait objects remains because it is needed until we
have DST.

This will break code like:

    fn foo(x: &int) { ... }

    let a = box 3i;
    foo(a);

Change this code to:

    fn foo(x: &int) { ... }

    let a = box 3i;
    foo(&*a);

[breaking-change]

r? @alexcrichton
@chris-morgan
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I’ve just discovered that [T, ..N] coerces to &mut [T] silently. Not sure if there’s any way to do this explicitly at present, though. Still, it should be dismantled.

@nrc nrc mentioned this issue Sep 1, 2014
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nrc added a commit to nrc/rust that referenced this issue Sep 2, 2014
@nrc
Remove cross-borrowing for traits.
7f72884 
Closes rust-lang#15349

[breaking-change]

Trait objects are no longer implicitly coerced from Box<T> to &T. You must make an explicit coercion using `&*`.
bors added a commit that referenced this issue Sep 3, 2014
@bors
auto merge of #16917 : nick29581/rust/cross-trait, r=pcwalton
f7ec95e 
Closes #15349

r? @pcwalton (or anyone else)
bors added a commit to rust-lang-ci/rust that referenced this issue Aug 7, 2023
@bors
Auto merge of rust-lang#15349 - lowr:fix/fn-def-display-source-code, …
3eba6d3 
…r=lnicola

Show anonymous fn def type as a fn pointer in source code

Fixes rust-lang#15346

The second commit is an unrelated change. I can remove it if not desired.
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Remove cross-borrowing for traits nrc/rust
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@lilyball @pcwalton @pnkfelix @chris-morgan