Rebind template(bug?)

[ag0aep6g via Digitalmars-d-learn]

On 08/22/2016 08:04 PM, Engine Machine wrote:
> How do you seriously think this is cleaner/simpler? You have two
> classes. Their is no uniformity between them. You have uniformity
> between all the derived classes then have a special case for the base
> class. A certain easy to follow pattern is set up but needlessly break
> it for one case. Why?

It avoids the relatively obscure (and badly named, by me) 
InstantiateOrEmptySeq template.

You can take this further with template constraints. Gives it a more 
uniform appearance at the price of some repetition:

----
class T()
{
     int x;
}

class T(A...) : T!(A[0..$-1])
     if (A.length > 0 && A[$-1] == "Animal")
{
     int y;
}

class T(A...) : T!(A[0..$-1])
     if (A.length > 0 && A[$-1] == "Dog")
{
     int z;
}

class T(A...) : T!(A[0..$-1])
     if (A.length > 0 && A[$-1] == "Pug")
{
     int s;
}
----

I wouldn't say that this is obviously, objectively, significantly better 
than the version with the helper template, though.

By the way, it's not obvious to me what this whole thing achieves in 
practice. And whatever benefit there is, it has to be weighed against 
the cost of the added complexity.

I don't mean to say that this is not worth pursuing. Just a friendly 
reminder that over-engineering is something to look out for, from 
someone who is prone to over-engineering himself.