More operators inside `is(...)` expressions

Stefan Koch uplink.coder at
Mon Aug 24 12:28:27 UTC 2020

On Monday, 24 August 2020 at 11:49:05 UTC, Steven Schveighoffer 
> On 8/24/20 4:03 AM, Timon Gehr wrote:
>> On 23.08.20 23:08, Per Nordlöw wrote:
>>> Why aren't more operators allowed inside 
>>> `is(...)`-expressions?
>>> For instance
>>>      if (!is(CommonType!(typeof(min), typeof(max)) == void))
>>> could be written as
>>>      if (is(CommonType!(typeof(min), typeof(max)) != void))
>>> .
>> So is(undefined != void) would be `true`? (Where `undefined` 
>> does not exist.)
> Yes. If you write !is(T == void), then you are already not 
> checking whether T is defined. This is no different.
> This literally is just a nicer way to write it, where the 
> operation is closer to the parameters, instead of partly 
> outside the expression.
> -Steve

The problems I see here are:

1) Complicating the rules for is expressions further
2) Adding a special syntax for what I perceive to be an uncommon 

I.E. (T != void) does not narrow your result set significantly.
The only place where you could write that is if your T-set is 
already narrowed down.
Or rather if you have a (T == void) specialization which you want 
to rule out.

I might be wrong here but I do think that's uncommon.

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