"llee" <llee@goucher.edu> wrote in message news:g6nq50$2b9n$1@digitalmars.com...
>I ran into a similar problem when working with sets. I could define sets using templates, but I couldn't define sets of sets without the compiler complaining about recursive definitions.
>
> For example:
>     class Set (T) { T[] elems; ... }
>
> but how would I define a set of sets?.
>
>     Set! (Set) family = ... does not work.

A set of sets of ... what?  You just need to specify what type it is.  "Set" is not a type, it is a template.

Set!(Set!(int)) family;

"llee" wrote
> I'm trying to define an object named Param that has a member named value.
> Value can be either a variable of type T, and array of type T[], or an
> array of other Params.
> Using templates, I could implement the first two cases:
>     class Param (T) { T value; ... }
> but I could not handle the recursive case.

enum valuetype
{
   T,
   Array,
   Param
}

class Param(T, valuetype vt = valuetype.T)
{
  static if(vt == valuetype.T)
  {
      T value;
  }
  else if(vt == valuetype.Array)
  {
      T[] value;
  }
  else if(vt == valuetype.Param)
  {
      Param!(T, vt) value;
  }
}

-Steve

Steven Schveighoffer:
> enum valuetype
> {
>    T,
>    Array,
>    Param
> }
> ...

That's an interesting solution, I'll probably find a way to use it myself.
It follows the old advice: when the type system of you language isn't powerful enough for your purposes, punch a hole in it an go on ;-)

As more and more "advanced" features are added to D 2.x, its type system may show some limitations (on the other hand in most situations I don't need a bulletproof type system like Haskell one).

Bye,
bearophile

On Tue, 29 Jul 2008 23:59:12 +0400, Jarrett Billingsley <kb3ctd2@yahoo.com> wrote:

> "llee" <llee@goucher.edu> wrote in message
> news:g6nq50$2b9n$1@digitalmars.com...
>> I ran into a similar problem when working with sets. I could define sets
>> using templates, but I couldn't define sets of sets without the compiler
>> complaining about recursive definitions.
>>
>> For example:
>>     class Set (T) { T[] elems; ... }
>>
>> but how would I define a set of sets?.
>>
>>     Set! (Set) family = ... does not work.
>
> A set of sets of ... what?  You just need to specify what type it is.  "Set"
> is not a type, it is a template.
>
> Set!(Set!(int)) family;
>
>

How about, say, Set of Set of the self type? So that it becomes this:

class MySet
{
	MySet[] elems;
	// ...
}

"Koroskin Denis" <2korden@gmail.com> wrote in message news:op.ue3up2utenyajd@proton.creatstudio.intranet...
>
> How about, say, Set of Set of the self type? So that it becomes this:
>
> class MySet
> {
> MySet[] elems;
> // ...
> }

I'm not entirely sure what you're asking.

class Set(T)
{
    T[] elems;
    this() { Stdout.formatln("set"); }
}

class Set(T : Set!(U), U)
{
    Set!(U) elems;
    this() { Stdout.formatln("set of sets"); }
}

void main()
{
    auto x = new Set!(Set!(int));
}

prints "set of sets".

Reply to Jarrett,

> "Koroskin Denis" <2korden@gmail.com> wrote in message
> news:op.ue3up2utenyajd@proton.creatstudio.intranet...
> 
>> How about, say, Set of Set of the self type? So that it becomes this:
>> 
>> class MySet
>> {
>> MySet[] elems;
>> // ...
>> }
> I'm not entirely sure what you're asking.
> 

he wants is(typeof(this) == typeof(this.elems[0]));

It will be a kind of tree.

"BCS" <ao@pathlink.com> wrote in message news:55391cb32fbe48cac041c4d5a41e@news.digitalmars.com...
> Reply to Jarrett,
>
>> "Koroskin Denis" <2korden@gmail.com> wrote in message news:op.ue3up2utenyajd@proton.creatstudio.intranet...
>>
>>> How about, say, Set of Set of the self type? So that it becomes this:
>>>
>>> class MySet
>>> {
>>> MySet[] elems;
>>> // ...
>>> }
>> I'm not entirely sure what you're asking.
>>
>
> he wants is(typeof(this) == typeof(this.elems[0]));
>
> It will be a kind of tree.

Ahh.