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Clarify unresolved questions in Span RFC #306

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May 21, 2018
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Clarify unresolved questions in Span RFC #306

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27 changes: 16 additions & 11 deletions RFCs/FS-1053-span.md
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Original file line number Diff line number Diff line change
Expand Up @@ -236,6 +236,22 @@ type S(count1: byref<int>, count2: byref<int>) =
* Using `inref<T>` in an abstract slot signature or implementation results in the automatic emit of an `modreq` attribute on an argument or return
* Using `outref<T>` in argument position results in the automatic emit of an `[Out]` attribute on the argument

### Overloading:

When an implicit address is being taken for an `inref` parameter, an overload with an argument of type `SomeType` is preferred to an overload with an argument of type `inref<SomeType>`. For example give this:
```
type C() =
static member M(x: System.DateTime) = x.AddDays(1.0)
static member M(x: inref<System.DateTime>) = x.AddDays(2.0)
static member M2(x: System.DateTime, y: int) = x.AddDays(1.0)
static member M2(x: inref<System.DateTime>, y: int) = x.AddDays(2.0)
let res = System.DateTime.Now
let v = C.M(res)
let v2 = C.M2(res, 4)
```
In both cases the overload resolves to the method taking `System.DateTime` rather than the one taking `inref<System.DateTime>`.


### Ignoring Obsolete attribute on `ByRefLike`

Separately, C# attaches an `Obsolete` attribute to the `Span` and `Memory` types in order to give errors in down level compilers seeing these types, and presumably has special code to ignore it. We add a corresponding special case in the compiler to ignore the `Obsolete` attribute on `ByRefLike` structs.
Expand Down Expand Up @@ -381,14 +397,3 @@ namespace System.Runtime.CompilerServices
[unresolved]: #unresolved-questions

None
* What happens if we have two overloads, e.g. in C#

```
void Deconstruct<T, U>(in this KeyValuePair<T, U> k, out T key, out U value) { .. }
void Deconstruct<T, U>(this KeyValuePair<T, U> k, out T key, out U value) { .. }
```

* How the overload resolution interop supposed to work between F# -> C# and C# -> F#? Original Source: See https://github.com/fsharp/fslang-suggestions/issues/648#issuecomment-390157352

* [the generated IL callwith will pass the x argument with an `[<Out>]` attribute](https://github.com/fsharp/fslang-design/issues/287#issuecomment-390203219), this looks incorrect