ref fields updates #6285
ref fields updates #6285
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Updates based on our deployment experiences
| @@ -245,8 +249,6 @@ Span<int> ScopedLocalExamples() | |||
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| Other uses for `scoped` on locals are discussed [below](#examples-scoped-locals). | |||
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| When `scoped` is applied to an instance method the `this` parameter will have the type `scoped ref T`. By default this is redundant as `scoped ref T` is the default type of `this`. It is useful in the case the `struct` is declared as `unscoped` (detailed [below](#return-fields-by-ref)). | |||
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As written felt like I was just mostly restating previous stuff. Expanded section above and removed this.
| Overall there are three `ref` location which are implicitly declared as `scoped`: | ||
| - `this` on a `struct` instance method | ||
| - `out` parameters | ||
| - `ref` parameters which refer to a `ref struct` |
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This default flip is easy to add to rules and fixes the last usability hurdle we had with ref fields. There are other alternatives we are exploring that would remove this special casing. Short term though wanted to focus on getting the rules tightened up as teams are locking down on implementations.
Next week we'll be exploing the other options to see if we can remove this special case.
| In addition to parameters the `scoped` annotation can be applied to locals or `struct` instance methods. These annotations have the same impact to lifetimes when applied to locals. For locals these annotations concretely define the lifetimes and override the lifetime that would be inferred via the initializer. | ||
| The `scoped` annotation can also be applied to the following locations: | ||
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| - locals: This annotation sets the lifetime as *safe-to-escape*, or *ref-safe-to-escape* in case of a `ref` local, to of *current method* irrespective of the initializer lifetime. |
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| The presence of `scoped` allows us to refine the rule to reduce the friction the rule creates. The `scoped` modifier lets us remove arguments from consideration as they cannot be returned from the method. | ||
| > For any method invocation | ||
| > 1. Calculate the *safe-to-escape* of the method return (for this rule assume it has a `ref struct` return) |
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It's because if it's a non-ref struct return then safe-to-escape of the return is trivially calling method. Effectively this is saying to "pretend" there is a ref struct return, calculate that safe-to-escape scope and then validate it can be assigned to every ref or out argument.
| The `scoped` annotation can also be applied to the following locations: | ||
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| - locals: This annotation sets the lifetime as *safe-to-escape*, or *ref-safe-to-escape* in case of a `ref` local, to of *current method* irrespective of the initializer lifetime. | ||
| - `struct` instance methods: This annotation sets the type of `this` to `scoped ref T`. This is the default value but it is useful in the case the overall `struct` type is declared as `unscoped` (detailed [below](#return-fields-by-ref)). |
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Is this still needed now that API review has disallowed adding [UnscopedRef] to a whole type? 🤔
See: dotnet/runtime#72074 (comment). I realize this PR has already been merged, but should we fix this?
Updates based on our deployment experiences