Why doesn't std.variant.visit automatically call the provided delegates?

[Kapps via Digitalmars-d]

On Saturday, 5 November 2016 at 10:09:55 UTC, Adam D. Ruppe wrote:
> On Saturday, 5 November 2016 at 08:27:49 UTC, Nemanja Boric 
> wrote:
>>     // This - does nothing
>>     variant.visit!(    (string s) => { enforce(false); x = 2; 
>> },
>
> It calls the function... which returns a delegate, which you 
> never called.
>
> This is one of the most common mistakes people are making: {} 
> in D is a delegate, and () => is a delegate, therefore () => {} 
> is a delegate that returns a delegate... usually NOT what you 
> want.
>
> What you wrote is equivalent to writing
>
> delegate() callback(string s) {
>    return delegate() {
>          enforce(false);
>          x = 2;
>    };
> }
>
>
> Do not use the => syntax if there is more than one expression. 
> You'll get what you want by simply leaving the => out:
>
>>
>>     // This works as expected
>>     variant.visit!(    (string s) { x = 2; },
>>                        (int i)    { x = 3; });

That's really confusing. I've used D for quite a while, and 
didn't know that. Admittedly I doubt I've ever tried () => { }, 
but given languages like C# which this syntax was partially taken 
from(?), that behaviour is very unexpected. That feels like it 
should be a compiler warning.