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Specify auto trait trait object upcasting #513

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Jul 8, 2024
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Specify auto trait trait object upcasting #513

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2 changes: 2 additions & 0 deletions src/changelog.rst
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Expand Up @@ -145,6 +145,8 @@ Language changes in Rust 1.78.0

* `\`trait Trait: Auto {}\`: allow upcasting from \`dyn Trait\` to \`dyn Trait + Auto\` <https://github.com/rust-lang/rust/pull/119338>`_

* New paragraph: :p:`fls_SYnFJBhi0IWj`

language changes in Rust 1.77.0
-------------------------------

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8 changes: 8 additions & 0 deletions src/glossary.rst
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Expand Up @@ -5057,6 +5057,14 @@ primitive representation
:dt:`Primitive representation` is the :t:`type representation` of
:t:`[integer type]s`.

.. _fls_mk3sa7OvtJvB:

principal trait
^^^^^^^^^^^^^^^

:dp:`fls_YtYOHoPaMPFX`
The :dt:`principal trait` of :t:`trait object type` is its first :t:`trait bound`.

.. _fls_v1u1mevpj0kj:

private visibility
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15 changes: 12 additions & 3 deletions src/types-and-traits.rst
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Expand Up @@ -1156,10 +1156,14 @@ Trait Object Types
A :t:`trait object type` is a :t:`type` that implements a :t:`trait`, where the
:t:`type` is not known at compile time.

:dp:`fls_eWac7zOda3lh`
The :t:`principal trait` of :t:`trait object type` is the first :t:`trait bound`.
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This definition isn't used not (thought I'd need the term when describing this at first), but it will become relevant in the future when full upcasting exists


:dp:`fls_9z8oleh0wdel`
The first :t:`trait bound` of a :t:`trait object type` shall denote an
:t:`object safe` :t:`trait`. Any subsequent :t:`[trait bound]s` shall denote
:t:`[auto trait]s`.
The :t:`principal trait` shall denote an :t:`object safe` :t:`trait`.

:dp:`fls_hJII8XYAtZeY`
All non-:t:`principal trait` :t:`[trait bound]s` shall denote :t:`[auto trait]s`.

:dp:`fls_s0oy2c8t4yz9`
A :t:`trait object type` shall not contain :t:`[opt-out trait bound]s`.
Expand Down Expand Up @@ -1992,6 +1996,11 @@ occur when:
The source :t:`type` is the :t:`never type` and the target :t:`type` is any
:t:`type`.

* :dp:`fls_SYnFJBhi0IWj`
The source :t:`type` is a :t:`trait object type` and the target :t:`type` is a
:t:`trait object type` with the same :t:`[trait bound]s` and additional
:t:`[auto trait]s`.

:dp:`fls_iiiu2q7pym4p`
An :t:`unsized coercion` is a :t:`type coercion` that converts a :t:`sized type`
into an :t:`unsized type`. :t:`Unsized coercion` from a source :t:`type` to a
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