is(x = module) vs. __traits(isModule, x)

[Steven Schveighoffer]

On 10/8/20 1:43 PM, Paul Backus wrote:
> On Thursday, 8 October 2020 at 16:49:50 UTC, Steven Schveighoffer wrote:
>>
>> If we got type functions, and have UFCS, isn't this as easy as e.g.:
>>
>> bool isModule(alias x) { return __traits(isModule, x); }
>>
>> static assert(std.stdio.isModule);
> 
> Ok, now do __traits(getMember, variable, "foo") and __traits(compiles, 
> expression). :)

I did getMember already.

And it can't do __traits(compiles). So, just use __traits(compiles) for 
that one.

> Using type functions to wrap __traits has the same issues as using 
> templates to wrap __traits. In the common case, it works, but in the 
> general case, it fails, because __traits have special privileges that no 
> other construct in the D language (including templates, functions, and 
> type functions) can fully imitate.

I'm not sure that's 100% true for type functions -- they aren't in there 
yet.

-Steve