Pattern matching: Callback For Matching Type

[Richard (Rikki) Andrew Cattermole]

On 30/05/2024 7:38 AM, Harry Gillanders wrote:
> 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.).

Yes. You would want this to protect your tag value so that it would be 
read only.

> 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);
> }
> ```

That could be a good reason to switch.

Although it can be done using a fallback ``(arg) { ... },`` instead.