Proposal: allow ref enumeration over arrays

[huoyaoyuan]

Proposed syntax:

void M(X[] a)
{
    foreach (ref X x in a)
    {

    }
}

Currently alternative:

void M(X[] a)
{
    foreach (ref X x in a.AsSpan())
    {

    }
}

Benifits:

Syntax completeness.
Can work if the Span type is not present.
Since array enumeration is specially treated by the compiler, the compiler can generate simpler code to reduce the stress of JIT. Currently JIT generate worse code when using AsSpan().

Risk

No risk:
Array is specially treated by the compiler. This feature should not require any member defined in metadata.
This is about introducing new binding rule, not new syntax.
The semantic is straight.

[YairHalberstadt]

I feel like it would be a better idea to open an issue on dotnet/runtime to improve the Jit.

[reflectronic]

This is still a hole in the language. I opened an issue about it a while ago, and it appears that the feature is a little half baked.