I dun a DIP, possibly the best DIP ever

[Steven Schveighoffer]

On 5/10/20 4:30 AM, Nick Treleaven wrote:
> On Friday, 24 April 2020 at 21:00:08 UTC, Steven Schveighoffer wrote:
>> import std.algorithm : canFind;
>> enum anySatisfy(alias F, T...) = [F!(T)...].canFind(true);
>> enum allSatisfy(alias F, T...) = ![F!(T)...].canFind(false);
> 
> That might be slower than the existing templates (now in 
> core.internal.traits), which don't use template recursion, and short 
> circuit:
> 
> template anySatisfy(alias F, Ts...)
> {
>      static foreach (T; Ts)
>      {
>          static if (!is(typeof(anySatisfy) == bool) && // not yet defined
>                     F!T)
>          {
>              enum anySatisfy = true;
>          }
>      }
>      static if (!is(typeof(anySatisfy) == bool)) // if not yet defined
>      {
>          enum anySatisfy = false;
>      }
> }

I admit, I didn't look at the implementation, I just assumed it was one 
of the recursive ones.

But the "performance" is relative to where the satisfying items are. But 
it's a good point, evaluating all of the templates to see if one is true 
leaves some performance on the table, and another reason to prefer a 
folding mechanism. i.e., this might short circuit automatically (if 
supported):

enum anySatisfy(alias F, T...) = F!(T) || ...;

> 
> Your versions also require an extra import (although canFind could be 
> locally copied).

Yeah, a for loop CTFE can easily be created for this if needed. It was 
just easier to reach for something that exists to show the brevity.

-Steve