Champion "ref extension methods on structs" (C# 7.2)

[gafter]

• Proposal added https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.2/readonly-ref.md
• Discussed in LDM
• Decision in LDM
• Finalized (done, rejected, inactive)
• Spec'ed

See also dotnet/roslyn#165

[Thaina]

Very important feature

[benaadams]

Precedent in VB.NET. Should be compatible? (Currently C# can't see VB.NET's byref extension methods)

Also should work with ref returns; which enables low cost fluent or functional struct apis

[orthoxerox]

See also #128 (ref operators (on structs))

[alrz]

What happens if we have two overloads,

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) { .. }

I think this should be possible to provide a ref variant without breaking existing code and the compiler should prefer the first overload afterwards.