Read only delegate

[Rene Zwanenburg via Digitalmars-d-learn]

On Monday, 4 April 2016 at 08:10:10 UTC, Edwin van Leeuwen wrote:
> Is there a way to make sure a delegate only reads state, 
> without changing it? I tried annotating the delegate as const, 
> but that does not seem to work.
> ```

Yeah this is a nasty old issue. The underlying problem is that a 
delegate's function and context pointers are completely untyped.

https://issues.dlang.org/show_bug.cgi?id=1983