Uncallable delegates

[Timon Gehr]

On 5/16/26 03:45, Walter Bright wrote:
> I've already acknowledged and filed a bug report with `pure` on delegates:
> 
> https://github.com/dlang/dmd/issues/23125
> ...

This is a completely unrelated issue. Not every code that has a 
soundness issue and also contains the `pure` keyword is the same problem.

> If the `pure` is necessary for your example issue, then that is the 
> problem.

No, that's just a part in the exploit chain that allows me to modify 
`immutable` data, because that is what you asked for.

> If it is not necessary, why is it there?
> ...

To allow converting the result to `immutable`.

The most obvious fix is to disallow calling a `immutable(T 
delegate(S))`, just like `const(T delegate(S))` must not be callable.

We should at the very least be able to agree on this, because this is 
how it works for classes.