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Rename LifetimeAnnotationAttribute to ScopedRefAttribute and remove unnecessary members #6325

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Jul 27, 2022
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Rename LifetimeAnnotationAttribute to ScopedRefAttribute and remove unnecessary members #6325

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Rename `LifetimeAnnotationAttribute` to `ScopedRefAttribute` and remo…
jcouv Jul 27, 2022
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Update low-level-struct-improvements.md
jcouv Jul 27, 2022
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Update low-level-struct-improvements.md
jcouv Jul 27, 2022
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jcouv Jul 27, 2022
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18 changes: 6 additions & 12 deletions proposals/low-level-struct-improvements.md
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Expand Up @@ -514,28 +514,22 @@ Detailed Notes:
- Any member that is not declared on a `struct`
- Any `static` member, `init` member or constructor on a `struct`

### LifetimeAnnotationAttribute
The `scoped` and `unscoped` annotations will be emitted into metadata via the type `System.Runtime.CompilerServices.LifetimeAttribute` attribute. This attribute will be matched by name meaning it does not need to appear in any specific assembly.
### ScopedRefAttribute
The `scoped` annotations will be emitted into metadata via the type `System.Runtime.CompilerServices.ScopedRefAttribute` attribute. This attribute will be matched by name meaning it does not need to appear in any specific assembly.

The type will have the following definition:

```c#
[AttributeUsage(AttributeTargets.Struct | AttributeTargets.Method | AttributeTargets.Property | AttributeTargets.Parameter)]
public sealed class LifetimeAnnotationAttribute : Attribute
namespace System.Runtime.CompilerServices
{
private int _value;
public bool IsScoped => _value == 1;

public LifetimeAnnotationAttribute(int value)
[AttributeUsage(AttributeTargets.Parameter, AllowMultiple = false, Inherited = false)]
internal sealed class ScopedRefAttribute : Attribute
{
_value = value;
}
}
```

The attribute uses `int` instead of `bool` to allow for future lifetime expansions in this space.

The compiler will emit this attribute on the element targeted by the `scoped` or `unscoped` syntax. This is true for types, methods and parameters. This will only be emitted when the syntax causes the value to differ from its default state. For example `scoped out` will cause no attribute to be emitted.
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This will only be emitted when the syntax causes the value to differ from its default state.

Consider keeping this sentence. (Sorry if my previous comment was confusing.)

The compiler will emit this attribute on the parameter with `scoped` syntax. This will only be emitted when the syntax causes the value to differ from its default state. For example `scoped out` will cause no attribute to be emitted.

### Safe fixed size buffers
The language will relax the restrictions on fixed sized arrays such that they can be declared in safe code and the element type can be managed or unmanaged. This will make types like the following legal:
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