Discussion Thread: DIP 1044--Enum Type Inference--Community Review Round 1

[Vladimir Panteleev]

On Friday, 18 November 2022 at 15:37:31 UTC, Mike Parker wrote:
> ## Discussion Thread
>
> This is the discussion thread for the first round of Community 
> Review of DIP 1044, "Enum Type Inference":

[half feedback, half random brainstorming, so posting here to be 
safe]

I would like to suggest the following changes for consideration:

- Replace the `$ Identifier` syntax with `: Identifier`, to match 
other languages like Ruby and Lisp.

- The `: Identifier` syntax creates a value of a dynamic 
pseudo-type (a bit like `typeof(null)`).

   - The type's name is `typeof(:Identifier)`.

   - The type has size 0 and holds a single value.

   - The type is implicitly convertible to any enum type which has 
a member with the same name as `Identifier`.

I think this is a more precise and immediately implementable 
definition of the mechanics. Not sure if a good thing or not, but 
this will also allow using `:keyword`s stand-alone, like in 
Ruby/Lisp in a congruent manner. For the purposes at hand (enum 
type inference), it will also allow passing through the 
short-hand identifier to templated and `auto` functions.

It will not allow

```d
myFn($a + $a); // passes A.b
```

to work, but I'm not sure that would be implementable anyway in a 
reasonable manner and provide justifiable value. I think the 
remaining examples in the DIP will continue to work.

On another point, since the DIP mentions the `with` approach, 
I'll mention that the workaround I've been using is to declare a 
short local alias for the enum type. At the top level (e.g. for 
variable/constant initializers), it can be done by wrapping the 
value in a CTFE function: 
https://gist.github.com/CyberShadow/54ca7a0fa594c2272cabf8677ff6e42f#file-game-d-L150