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Stabilize Rc, Arc and Pin as method receivers #56805

Merged
merged 3 commits into from
Dec 22, 2018
Merged

Stabilize Rc, Arc and Pin as method receivers #56805

merged 3 commits into from
Dec 22, 2018

Commits on Dec 20, 2018

  1. Stabilize Rc, Arc and Pin as method receivers 

    This lets you write methods using `self: Rc<Self>`, `self: Arc<Self>`, `self: Pin<&mut Self>`, `self: Pin<Box<Self>`, and other combinations involving `Pin` and another stdlib receiver type, without needing the `arbitrary_self_types`. Other user-created receiver types can be used, but they still require the feature flag to use.

This is implemented by introducing a new trait, `Receiver`, which the method receiver's type must implement if the `arbitrary_self_types` feature is not enabled. To keep composed receiver types such as `&Arc<Self>` unstable, the receiver type is also required to implement `Deref<Target=Self>` when the feature flag is not enabled.

This lets you use `self: Rc<Self>` and `self: Arc<Self>` in stable Rust, which was not allowed previously. It was agreed that they would be stabilized in rust-lang#55786. `self: Pin<&Self>` and other pinned receiver types do not require the `arbitrary_self_types` feature, but they cannot be used on stable because `Pin` still requires the `pin` feature.
    @mikeyhew
    mikeyhew committed Dec 20, 2018
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  2. add a doc comment on receiver_is_valid

    @mikeyhew
    mikeyhew committed Dec 20, 2018
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  3. Refactor and add comments to code in receiver_is_valid 

    also updated some error messages

removed the code manually checking for `receiver_ty: Deref<Target=self_ty>`, in favour of using autoderef but only doing one iteration. This will cause error messages to be more consistent. Before, a "mismatched method receiver" error would be emitted when `receiver_ty` was valid except for a lifetime parameter, but only when `feature(arbitrary_self_types)` was enabled, and without the feature flag the error would be "uncoercible receiver". Now it emits "mismatched method receiver" in both cases.
    @mikeyhew
    mikeyhew committed Dec 20, 2018
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