Update RuntimeHelpers.Await rules
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These rules now clarify the extensibility point we're looking to establish with the runtime for `Await` helpers. Generally speaking, these are just ordinary methods that a user is free to call, so there's no issue with us using them for subtypes of `Task`, since the user could write that themselves and the runtime will have to handle it.
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jcouv
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Apr 2, 2025
| For any lvalue of one of these types, we'll generally rewrite `await expr` into `System.Runtime.CompilerServices.RuntimeHelpers.Await(expr)`. A number of different example scenarios for this are covered below. The | ||
| #### `RuntimeHelpers.Await` Scenarios | ||
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| The for any `await expr` with type `E`, the compiler will attempt to match it to a helper method in `System.Runtime.CompilerServices.RuntimeHelpers`. The following algorithm is used: |
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nit: the sentence suggests that await expr has type E, but you mean that expr has type E.
jcouv
reviewed
Apr 2, 2025
| 2. If `Mi` takes more than 1 parameter (named `P`), it is removed. | ||
| 3. If `Mi` has a generic arity of 0, all of the following must be true, or `Mi` is removed: | ||
| 1. The return type is `System.Void` | ||
| 2. There is an identity or implicit reference conversion from `E` to the type of `P`. |
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These rules now clarify the extensibility point we're looking to establish with the runtime for
Awaithelpers. Generally speaking, these are just ordinary methods that a user is free to call, so there's no issue with us using them for subtypes ofTask, since the user could write that themselves and the runtime will have to handle it.