FS-1053 update :: Support instantiation of C#-defined "allows ref struct" generics with ByrefLike types #787
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| * Cannot be captured by any closure construct (async methods or lambda expressions) | ||
| * Cannot be used as a generic parameter | ||
| - In F# 9 and higher, this restriction is relaxed if the generic parameter is defined in C# using the `allows ref struct` anti-constraint. F# can instantiate such generics in types and methods with byref-like types. As a few examples, this affects BCL delegate types (`Action<>`,`Func<>`), interfaces (`IEnumerable<>`,`IComparable<>`) and generic arguments with a user-provided accumulator function (`String.string Create<TState>(int length, TState state, SpanAction<char, TState> action)`) | ||
| - It is impossible to author generic code supporting byref-like types in F#. |
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Would it be worth expanding on this here? E.g., to mention that the allows ref struct anti-constraint is not automatically propagated in the same way as normal generic constraints, with some examples.
let a : Action<'T> = …
let f (x : 'T) = a.Invoke x // Can 'T be ReadOnlySpan<int> here? Presumably not?let f (g : Action<'T>) (x : 'T) = g.Invoke x // Can 'T be ReadOnlySpan<int> here?
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It is not automatically propagated, this makes sense to expand on - thanks for checking this.
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