• deed (29/29) Jun 22 2013 class A { ... }
• Simen Kjaeraas (10/38) Jun 22 2013 The type of an expression in D is determined at compile time, and getO
• deed (2/4) Jun 22 2013 Thanks Simen.

"deed" <none none.none> writes:

class A                  { ... }
class NonContainer : A   { ... }
class Container : A      { A[] container; }
class NC1 : NonContainer {}
...
class C1 : Container {}
...

A getO(string info)
{
     switch (info)
     {
         default     : return new NonContainer();
         case "info1": return new C1();
         case "info2": return new NC1();
         case "info3": return new Container();
         case "info4": return new NonContainer();
         ...
     }
}

void foo()
{
     auto o = getO("some information");
     if (is(typeof(o) == Container) { ... }  // Doesn't work.
                                             // Type is always A.
     ...
}

Is there a way to make getO return the most specialized type of 
the instantiated object in the switch statement to enable this 
pattern?

"Simen Kjaeraas" <simen.kjaras gmail.com> writes:

On Sat, 22 Jun 2013 18:58:22 +0200, deed <none none.none> wrote:

 class A                  { ... }
 class NonContainer : A   { ... }
 class Container : A      { A[] container; }
 class NC1 : NonContainer {}
 ...
 class C1 : Container {}
 ...

 A getO(string info)
 {
      switch (info)
      {
          default     : return new NonContainer();
          case "info1": return new C1();
          case "info2": return new NC1();
          case "info3": return new Container();
          case "info4": return new NonContainer();
          ...
      }
 }

 void foo()
 {
      auto o = getO("some information");
      if (is(typeof(o) == Container) { ... }  // Doesn't work.
                                              // Type is always A.
      ...
 }

 Is there a way to make getO return the most specialized type of the  
 instantiated object in the switch statement to enable this pattern?

The type of an expression in D is determined at compile time, and getO
returns an A. Hence, o will always have static type A, and is(typeof(...
only checks the static type.

If you want to check the dynamic (run-time) type of o, you should
instead see if it is castable to Container:

     auto o = getO("info3");
     if (cast(Container)o != null) { ... }

-- 
Simen

"deed" <none none.none> writes:

     auto o = getO("info3");
     if (cast(Container)o != null) { ... }

Thanks Simen.
(Compiler requires !is instead of !=)