• llee (4/4) Jul 29 2008 Is there any way to instantiate a recursive template object. For example...
• Jarrett Billingsley (3/7) Jul 29 2008 What are you trying to do? Why didn't you post this in d.learn?
• llee (4/4) Jul 29 2008 I'm trying to define an object named Param that has a member named value...
• Steven Schveighoffer (23/29) Jul 29 2008 enum valuetype
• bearophile (6/13) Jul 29 2008 That's an interesting solution, I'll probably find a way to use it mysel...
• llee (5/5) Jul 29 2008 I ran into a similar problem when working with sets. I could define sets...
• BCS (3/13) Jul 29 2008 that might be a good thing
• Jarrett Billingsley (5/12) Jul 29 2008 A set of sets of ... what? You just need to specify what type it is. "...
• Koroskin Denis (8/24) Jul 30 2008 How about, say, Set of Set of the self type? So that it becomes this:
• Jarrett Billingsley (18/24) Jul 30 2008 I'm not entirely sure what you're asking.
• BCS (3/15) Jul 30 2008 he wants is(typeof(this) == typeof(this.elems[0]));
• Jarrett Billingsley (3/18) Jul 30 2008 Ahh.
• BCS (8/17) Jul 29 2008 No, there is no reason that you can't work with such a type but the synt...
• Oliver Dathe (2/3) Jul 29 2008 You seem to have forgotten something:
• llee (2/7) Jul 29 2008 That's what I need to know. I don't know what to put there to allow comp...
• Bill Baxter (10/18) Jul 29 2008 Since the thing you end up with is a template still, you have to define ...
• llee (1/1) Jul 29 2008 Actually, I should probably use tuples.

llee <llee goucher.edu> writes:

Is there any way to instantiate a recursive template object. For example:

class Param (T) { T values; ... }

...

Param! (Param) composite = new Param! (Param) ();

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"llee" <llee goucher.edu> wrote in message 
news:g6nmer$23ke$1 digitalmars.com...
 Is there any way to instantiate a recursive template object. For example:

 class Param (T) { T values; ... }

 ...

 Param! (Param) composite = new Param! (Param) ();

What are you trying to do?  Why didn't you post this in d.learn? 

llee <llee goucher.edu> writes:

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.

"Steven Schveighoffer" <schveiguy yahoo.com> writes:

"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 

bearophile <bearophileHUGS lycos.com> writes:

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

llee <llee goucher.edu> writes:

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.

BCS <ao pathlink.com> writes:

Reply to llee,

 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?.

that might be a good thing
sets of sets = strange things: http://en.wikipedia.org/wiki/Russell's_paradox

 
 Set! (Set) family = ... does not work.
 

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"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; 

"Koroskin Denis" <2korden gmail.com> writes:

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;
	// ...
}

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"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". 

BCS <ao pathlink.com> writes:

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.

"Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:

"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. 

BCS <ao pathlink.com> writes:

Reply to llee,

 Is there any way to instantiate a recursive template object. For
 example:
 
 class Param (T) { T values; ... }
 
 ...
 
 Param! (Param) composite = new Param! (Param) ();
 

No, there is no reason that you can't work with such a type but the syntax 
and type system internals make it impossible in practice.

You might be able to work around this with some combination of alias's
templates 
tart resolve to types and other hacks. 

The simplest option might be something like this:

class Param (T) { ... }
class P2 : Param!(P2) {}

Oliver Dathe <o.dathe gmx.de> writes:

 Param! (Param) composite = new Param! (Param) ();

You seem to have forgotten something:

... = new Param!( Param!(MISSING) );

llee <llee goucher.edu> writes:

Oliver Dathe Wrote:

 Param! (Param) composite = new Param! (Param) ();

 
 You seem to have forgotten something:
 
 ... = new Param!( Param!(MISSING) );

That's what I need to know. I don't know what to put there to allow composite
to be an array of arbitrary Params.

"Bill Baxter" <wbaxter gmail.com> writes:

Content-Disposition: inline

On Wed, Jul 30, 2008 at 4:36 AM, llee <llee goucher.edu> wrote:

 Oliver Dathe Wrote:

 Param! (Param) composite = new Param! (Param) ();

 You seem to have forgotten something:

 ... = new Param!( Param!(MISSING) );

 That's what I need to know. I don't know what to put there to allow
 composite to be an array of arbitrary Params.

Since the thing you end up with is a template still, you have to define a
new template that defines the alias you want:

  template SetOfSets(T) {  alias Set!(Set!(T)) SetOfSets; }

This is one place where D could be nicer.   I think extending the template
shortcut syntax to aliases would be nice:

   alias(T) Set!(Set!(T)) SetOfSets!(T);

It works for classes, structs and functions -- why not aliases too?

--bb

llee <llee goucher.edu> writes:

Actually, I should probably use tuples.