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?

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
> ...

Doh, title should of course be

I just discovered an alternative use of `is`-expressions.

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

On Thursday, 6 August 2020 at 22:24:43 UTC, Paul Backus wrote:
> [1] https://dlang.org/spec/expression.html#is_expression

Thanks

On Thursday, 6 August 2020 at 22:24:43 UTC, Paul Backus wrote:
> [1] https://dlang.org/spec/expression.html#is_expression

I bet there a several places in Phobos where this feature isn't but could be used.

On Friday, 7 August 2020 at 21:02:03 UTC, Per Nordlöw wrote:
> On Thursday, 6 August 2020 at 22:24:43 UTC, Paul Backus wrote:
>> [1] https://dlang.org/spec/expression.html#is_expression
>
> I bet there a several places in Phobos where this feature isn't but could be used.

I feel same. That there's a clever use of certain D features waiting to be discovered.

On Fri, Aug 07, 2020 at 09:02:03PM +0000, Per Nordlöw via Digitalmars-d-learn wrote:
> On Thursday, 6 August 2020 at 22:24:43 UTC, Paul Backus wrote:
> > [1] https://dlang.org/spec/expression.html#is_expression
> 
> I bet there a several places in Phobos where this feature isn't but could be used.

Perhaps. But as I recall, it's widely used throughout Phobos, so it probably won't be easy to find a place where it could be used but isn't.


T

-- 
Written on the window of a clothing store: No shirt, no shoes, no service.

On Thursday, 6 August 2020 at 22:24:43 UTC, Paul Backus wrote:
> [1] https://dlang.org/spec/expression.html#is_expression

Thanks