I'm going through Adam Wilson's talk 'C# to D' and I've gotten hung up by one of his examples regarding generic programming in D. Specifically, I'm trying to implement the code example found here: http://youtu.be/6_xdfSVRrKo?t=16m44s.

I created a templateExp.d file that looks like this:

	public class BaseClass {}
	public class OtherClass : BaseClass {}

	class SomeClass(T : BaseClass)
	{
		public T[] values;
		public void add(T input) { values ~= input; }
	}

	void main()
	{
		auto sc = new SomeClass();
		OtherClass oc1 = new OtherClass();
		OtherClass oc2 = new OtherClass();

		sc.add(oc1);
		sc.add(oc2);

		import std.stdio;
		writefln("value count", sc.values.length);
	}

When I run the dmd compiler, I get this error:

	>dmd templateExp.d
	teamplteExp.d(12): Error: class teamplteExp.SomeClass(T : BaseClass) is used as a type

How can I initialize this class correctly?

> When I run the dmd compiler, I get this error:
>
> 	>dmd templateExp.d
> 	teamplteExp.d(12): Error: class teamplteExp.SomeClass(T : BaseClass) is used as a type
>

This is actually:
	templateExp.d(12): Error: class templateExp.SomeClass(T : BaseClass) is used as a type

On Saturday, 5 July 2014 at 16:47:32 UTC, quakkels wrote:
> I'm going through Adam Wilson's talk 'C# to D' and I've gotten hung up by one of his examples regarding generic programming in D. Specifically, I'm trying to implement the code example found here: http://youtu.be/6_xdfSVRrKo?t=16m44s.
>
> I created a templateExp.d file that looks like this:
>
> 	public class BaseClass {}
> 	public class OtherClass : BaseClass {}
>
> 	class SomeClass(T : BaseClass)
> 	{
> 		public T[] values;
> 		public void add(T input) { values ~= input; }
> 	}
>
> 	void main()
> 	{
> 		auto sc = new SomeClass();
> 		OtherClass oc1 = new OtherClass();
> 		OtherClass oc2 = new OtherClass();
>
> 		sc.add(oc1);
> 		sc.add(oc2);
>
> 		import std.stdio;
> 		writefln("value count", sc.values.length);
> 	}
>
> When I run the dmd compiler, I get this error:
>
> 	>dmd templateExp.d
> 	teamplteExp.d(12): Error: class teamplteExp.SomeClass(T : BaseClass) is used as a type
>
> How can I initialize this class correctly?

try SomeClass (T): BaseClass

> try SomeClass (T): BaseClass

Not sure which line you want me to change. I don't want SomeClass to inherit from BaseClass. Rather, I want T to be restricted to classes that inherit from BaseClass.

When I change `class SomeClass(T : BaseClass)` to `class SomeClass(T) : BaseClass` I still get the "class templateExp.SomeClass(T) is used as a type" error.

On Saturday, 5 July 2014 at 17:17:03 UTC, quakkels wrote:
>> try SomeClass (T): BaseClass
>
> Not sure which line you want me to change. I don't want SomeClass to inherit from BaseClass. Rather, I want T to be restricted to classes that inherit from BaseClass.
>
> When I change `class SomeClass(T : BaseClass)` to `class SomeClass(T) : BaseClass` I still get the "class templateExp.SomeClass(T) is used as a type" error.

ah, sorry, I misunderstood. It looks like you need to change the lin

auto sc = new SomeClass ();

to

auto sc = new SomeClass!BaseClass ();

The compiler complains because SomeClass is a template when you call SomeClass() without !() template parameters. It only becomes a type once instantiated with parameters.

> ah, sorry, I misunderstood. It looks like you need to change the lin
>
> auto sc = new SomeClass ();
>
> to
>
> auto sc = new SomeClass!BaseClass ();
>
> The compiler complains because SomeClass is a template when you call SomeClass() without !() template parameters. It only becomes a type once instantiated with parameters.

Thanks. That did it.

Here's my working program.

	public class BaseClass {}
	public class OtherClass : BaseClass {}

	class SomeClass(T : BaseClass)
	{
		public T[] values;
		public void add(T input) { values ~= input; }
	}

	void main()
	{
		auto sc = new SomeClass!BaseClass();
		OtherClass oc1 = new OtherClass();
		OtherClass oc2 = new OtherClass();

		sc.add(oc1);
		sc.add(oc2);

		import std.stdio;
		writefln("value count: %d", sc.values.length);
	}