Rebind template(bug?)

[Engine Machine via Digitalmars-d-learn]

On Monday, 22 August 2016 at 07:54:36 UTC, Jack Applegame wrote:
> On Monday, 22 August 2016 at 00:43:00 UTC, Engine Machine wrote:
>> The following code works and does what I want!
>>
>> template InstantiateOrEmptySeq(alias tmpl, args...)
>> {
>>     alias Seq(T...)=T;
>>     static if (args.length > 0)
>>         alias InstantiateOrEmptySeq = tmpl!(args[0 .. $-1]);
>>     else
>>         alias InstantiateOrEmptySeq = Seq!();
>> }
>>
>>
>> class T(A...) : InstantiateOrEmptySeq!(T, A)
>> {	
>> 	static if (A.length == 0)
>> 	{
>>                 // Base class
>> 		int x;
>> 	} else	
>> 	static if (A[$-1] == "Animal")
>> 	{
>> 		int y;
>> 	} else
>> 	static if (A[$-1] == "Dog")
>> 	{
>> 		int z;
>> 	} else
>> 	static if (A[$-1] == "Pug")
>> 	{
>> 		int s;
>> 	} else static assert(A[$-1]~" not a defined class of 
>> "~this.stringof);
>> }
>
> Why don't you like a cleaner (in my opinion) solution?
>
> class T() {
> 	// Base class
> 	int x;
> }
>
> class T(A...) : T!(A[0..$-1]) {	
> 	static if (A[$-1] == "Animal")
> 	{
> 		int y;
> 	} else
> 	static if (A[$-1] == "Dog")
> 	{
> 		int z;
> 	} else
> 	static if (A[$-1] == "Pug")
> 	{
> 		int s;
> 	} else static assert(A[$-1]~" not a defined class of 
> "~this.stringof);
> }

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?