DIPX: Enum Literals / Implicit Selector Expression

[Timon Gehr]

On 7/6/22 20:30, Walter Bright wrote:
> On 7/5/2022 4:19 PM, Timon Gehr wrote:
>> I.e., in terms of type checking, everything has already been figured 
>> out and works:
> 
> That example just hurts my brain :-/

Well, I don't recommend people use that specific pattern, but it makes a 
lot of sense that it works in this way.

`x=>x` type checks as a `T delegate(T)` for any `T`.

`(x){}` does not type check as a `T delegate(T)` for any `T`.

The delegate literal is polysemous, and when trying to determine 
matches, it's instantiated for each potential match. Therefore, if a 
function accepts a `T delegate(T)`, the lambda can decide with `static 
if` if there is a match or not, arbitrarily depending on `T`.

(Note that all instantiations have to type check, as D does not have 
SFINAE.)