Pattern matching: Callback For Matching Type

[Harry Gillanders]

On Wednesday, 29 May 2024 at 18:24:19 UTC, Richard (Rikki) Andrew 
Cattermole wrote:
> Today I woke up and found I wanted to write up a proposal for 
> pattern matching for D.
>
> Permanent: 
> https://gist.github.com/rikkimax/79cbe199618b3f99104f7df2fc2a9681/e0e6dd44f7477be962e6c71312ba08a1fe1ee8d6
> Latest: 
> https://gist.github.com/rikkimax/79cbe199618b3f99104f7df2fc2a9681


> A __tag member must evaluate to an integer

Does this mean `__tag` can also be a member-function? For types 
where the tag doesn't need any storage (like NaN-boxing, disjoint 
enums, etc.).


I think it would be nice if the match-patterns were semicolon 
delimited, so that `static if` and `static foreach` and whatnot 
could be used in a `match` block—something like:

```d
mtu1.match {
	static if (condition) {
		(float v) => writeln("a float! ", v);
	}

	static foreach (T; Types) {
		(T v) => writeln(T.stringof, " ", v);
	}

	v => writeln("catch all! ", v);
}
```