Interfaces and Template Specializations

[Björn T. Herzig]

dsimcha Wrote:

> == Quote from Björn_T._Herzig (raichoo at googlemail.com)'s article
> > Hi,
> > I've been trying out D lately and stumbled upon the following problem.
> > I have 2 interfaces:
> > interface Plugable
> > {
> > 	public void plug();
> > }
> > interface Printable
> > {
> > 	public void print();
> > }
> > and two classes that implement those named Test which implements Plugable and
> Printable, and Test2 which only implements Plugable.
> > I now want to create a generic function with two specializations.
> > void tester(U)(U u) if (is(U : Plugable) && is(U : Printable))
> > {
> > 	writefln("U : Printable, Plugable");
> > 	u.plug();
> > 	u.print();
> > }
> > void tester(U : Printable)(U u)
> > {
> > 	writefln("U : printable");
> > 	u.print();
> > }
> > First of all this doesn't compile with the dmd 2.014 compiler since it doesn't
> accept the if statement after the template declaration (Or did I do something
> wrong?).
> 
> http://digitalmars.com/d/2.0/changelog.html#new2_015
> 
> This syntax is called constraints.  It didn't exist before 2.015.  The info on
> some pages is outdated.  The latest DMD version is 2.023.
> 
> > Another thing is that it's really weird syntax. In the second
> > specialization it's enough to write U : Plugable but it's not
> > possible to write something like void tester(U : Printable, Plugable)(U u) since
> Plugable would be handled as a second template parameter (or am I mistaken?).
> Wouldn't it be much nicer if you could write something like this : void tester(U :
> (Plugable, Printable))(U u) and void tester(U : (Plugable))(U u)? This way it
> would be possible to use a unified syntax for both cases without the need for a
> special case with the if-statement.
> 
> The weird syntax is because the first case is a constraint and the second is a
> template specialization.  For consistency, it might be better to just use
> constraints for everything.
> 
> Overall, though, D2's compile-time reflection system grew very organically and has
> a lot of duplicated features.  There's been some discussion in the past about how
> to reduce this complexity by removing redundancy.  You may have stumbled on one
> here:  Constraints, as far as I can tell, are just a more general case of template
> specialization.  Maybe we don't need template specialization anymore.

Thanks,

where can I get that version? I'm currently using dmd_2.014-052208_i386.deb from the download page. never saw a newer version. Right now my only possibility to use D is inside of an ubuntu vm which is not really the greatest way... i'd really like to know if dmd will be ported to Solaris.

Regards,
Björn