Roslyn: Please allow ref on foreach variable in case of an array

[alrz]

foreach(ref var item in array)
{
}

->

for(int i = 0; i < array.Length; ++i)
{
  ref var item = ref array[i];
}

[jnm2]

This is genius.

[HaloFour]

I assume that item would be readonly?

[DavidArno]

@HaloFour,

That seems extremely unlikely, given the team's resistance to making anything read-only by default.

In fact, the only use-case I can think of for this would be:
cs foreach(ref var item in array) { item = some new value; }
which would mean it would be useless if read-only. Unless I'm missing the obvious as usual... 😊

[alrz]

@jnm2 It is actually C++. :)

@HaloFour Since this would be only allowed for arrays, it is totally safe to be assigned. I think that's the case for readonly ref which doesn't exist yet.

@DavidArno It is currently readonly for non-ref case, which is a good thing. But in this case we explicitly declared it as ref so I don't think that would come as a surprise. Also, when it's ref it is already guarded against closure capture etc. readonly ref would not be useless; it avoids copying but still readonly.

[HaloFour]

@DavidArno

That seems extremely unlikely, given the team's resistance to making anything read-only by default.

Except for foreach iterator variables, which have always been readonly. That's explicitly why I mentioned it.

[jaredpar]

In order to make that readonly we'd need to support the notion of readonly ref. That is actually something we're looking into seriously for the next version of C#.

[eyalsk]

@jaredpar You mean like the next major release?

[jaredpar]

@eyalsk it will not be a part of C# 7.0. But it is a candidate for coming out in a point release / VS update.

[eyalsk]

@jaredpar Thank you very much.

[aluanhaddad]

@alrz

@jnm2 It is actually C++. :)

😆 😆
It won't be until we have
C# foreach(ref ref var item in array) { ... }
pure gold

[alrz]

Moved to https://github.com/dotnet/csharplang/issues/461