allow attributes & modifiers on a tuples fields

[lucasmeijer]

We'd love to be able to write the following code:
struct transform { public float x; }
struct rigidbody { public float x; }

    static void Main()
    {
        EntityEnumerator<T> GetEntities<T>() =>/*.....*/

        foreach(var entity in GetEntities<(readonly ref transform t, rigidbody r)>()
        {
            entity.r.x++;
            entity.t.x++;  //<-- compiler error, field t of the tuple is a readonly field
        }
    }

In the same vain, we also have some attributes we'd love to be able to place:

           foreach(var entity in GetEntities<(transform t, [Prioritize] rigidbody r)>()

I realize we can make an ad-hoc struct, and put the readonly modifier or attribute on there, but it would be amazing to be able to use the concise new tuple syntax.

[svick]

What would that compile to? Tuples use the System.ValueTuple family of types, which means there is no way to place attributes on them.

And even with #1147, you would need a version of ValueTuple for all the possible combinations of readonly and ref if you wanted modifiers to work. I don't think that's realistic.

[iam3yal]

@lucasmeijer The Records feature would give you more flexibility, it's not going to be tuples in anyway but you could at least put attributes on members but that's the future. :)