with and checked with expression?

[Seb via Digitalmars-d]

On Tuesday, 24 May 2016 at 19:03:11 UTC, ArturG wrote:
> would something like this be usefull?

A general word of advice - try to keep your post short & concise. 
It is more likely to get replies then.

Yes it would be to me, but I am not sure whether it would justify 
the rather uncommon #{} syntax. Does any language out there use 
it?

For the expression?, imho it is very useful - existence checks 
are very common. I know that at least ruby and CoffeeScript have 
it. Do you know more?