Hi All,

can D check, whether a class A an Interface B supports?

like:

  if (supports(class_A, intf_B))
  {
     cast(intf_B) (class_A).hello();
  }

--Qian

Qian Xu wrote:

> Hi All,
> 
> can D check, whether a class A an Interface B supports?
> 
> like:
> 
>   if (supports(class_A, intf_B))
>   {
>      cast(intf_B) (class_A).hello();
>   }
> 
> --Qian

what I have found is:

  if (is(class_A == intf_B))
  {
    cast(intf_B) (class_A).hello();
  }

Is there any better one?

--Qian

Qian Xu wrote:
> Hi All,
> 
> can D check, whether a class A an Interface B supports?
> 
> like:
> 
>   if (supports(class_A, intf_B))

    if (is(class_A : intf_B))
tests if 'class_A' is implicitly convertible to 'intf_B'. If the first is a class and the second an interface, that's equivalent to the class implementing the interface.

On Wed, Jan 21, 2009 at 10:30 AM, Qian Xu <quian.xu@stud.tu-ilmenau.de> wrote:
> Hi All,
>
> can D check, whether a class A an Interface B supports?
>
> like:
>
>  if (supports(class_A, intf_B))
>  {
>     cast(intf_B) (class_A).hello();
>  }

At compile time, like Frits said, you can use is(class_A : intf_B).

At runtime, you can use cast(intf_B)someInstance.  That returns 'null' if someInstance does _not_ inherit from intf_B.

if(auto i = cast(intf_B)instanceOfA)
    i.hello();

Frits van Bommel wrote:

> Qian Xu wrote:
>> Hi All,
>> 
>> can D check, whether a class A an Interface B supports?
>> 
>> like:
>> 
>>   if (supports(class_A, intf_B))
> 
>      if (is(class_A : intf_B))
> tests if 'class_A' is implicitly convertible to 'intf_B'. If the first
> is a class and the second an interface, that's equivalent to the class
> implementing the interface.

Thanks. Could you tell me, how to make a function for this? I do not know how to pass an Interface as parameter.

like
  bool supports(T)(T obj, interface_type t)
  {
    return (is(obj : t));
  }

Qian Xu schrieb:
> Thanks. Could you tell me, how to make a function for this? I do not know
> how to pass an Interface as parameter.
> 
> like
>   bool supports(T)(T obj, interface_type t)
>   {
>     return (is(obj : t));
>   }

Guess something like

bool supports(T, I) (T obj)
{
	return (is(obj : I));
}

should do it.

Reply to Qian,

> Frits van Bommel wrote:
> 
>> Qian Xu wrote:
>> 
>>> Hi All,
>>> 
>>> can D check, whether a class A an Interface B supports?
>>> 
>>> like:
>>> 
>>> if (supports(class_A, intf_B))
>>> 
>> if (is(class_A : intf_B))
>> tests if 'class_A' is implicitly convertible to 'intf_B'. If the
>> first
>> is a class and the second an interface, that's equivalent to the
>> class
>> implementing the interface.
> Thanks. Could you tell me, how to make a function for this? I do not
> know how to pass an Interface as parameter.
> 
> like
> bool supports(T)(T obj, interface_type t)
> {
> return (is(obj : t));
> }

Given 

> interface I {}
> class C1 {}
> class C2 : C1, I {}
> class C3 : C1 {}

if you want to check if an instance of C1 is a derived class that implements I use this

> null !is cast(I)c1

if you want it in a function

> bool IsA(TI, TC)(TC c)
> {
>   return null !is cast(TI)c;
> }