I just discovered an alternative use of the `in`-operator

[Paul Backus]

On Thursday, 6 August 2020 at 21:50:06 UTC, Per Nordlöw wrote:
> I just discovered that the is-operator can be used as in
>
> template ElementType(R)
> {
>     static if (is(typeof(R.init.front.init) T))
>         alias ElementType = T;
>     else
>         alias ElementType = void;
> }
>
> . Very powerful. Is this documented?

Yes, in the following paragraph under "IsExpression" [1]:

> Identifier is declared to be an alias of the resulting type if 
> the condition is satisfied. The Identifier forms can only be 
> used if the IsExpression appears in a StaticIfCondition.

[1] https://dlang.org/spec/expression.html#is_expression