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digitalmars.D.learn - Is this bug or not?

reply =?UTF-8?B?TWFyaXVzeiBHbGl3acWEc2tp?= <alienballance gmail.com> writes:
Is this bug, or is it as supposed to be? I'm not sure...
<code>
interface TmpI(T) {
     void func(T);
}

class TmpC {}
class TmpC2 : TmpC {}

class Tmp : TmpI!TmpC2 {
     void func(TmpI!TmpC) {};
}
void main(string[] args) {
     auto inst = new Tmp;
     inst.func(new Tmp);
}
</code>
Error: function tmp.Tmp.func (TmpI _param_0) is not callable using 
argument types (Tmp)
Error: cannot implicitly convert expression (new Tmp) of type tmp.Tmp to 
tmp.TmpI!(TmpC).TmpI
May 06 2011
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Fri, 06 May 2011 03:39:31 -0400, Mariusz Gliwiński  
<alienballance gmail.com> wrote:


 Is this bug, or is it as supposed to be? I'm not sure...
 <code>
 interface TmpI(T) {
      void func(T);
 }

 class TmpC {}
 class TmpC2 : TmpC {}

 class Tmp : TmpI!TmpC2 {
      void func(TmpI!TmpC) {};


Here is one problem, TmpI is instantiated with TmpC2 as the func  
parameter, yet you use TmpI!TmpC as your func parameter.  The func  
parameter should be TmpC2.  I'm surprised this part would compile without  
complaining that you didn't implement func.  But it probably would fail if  
it got to that check.


 }
 void main(string[] args) {
      auto inst = new Tmp;
      inst.func(new Tmp);


Here is the real problem, Tmp is not a TmpI!TmpC2, it's a TmpI!TmpC.  So  
it cannot be cast (implicitly or explicitly).  Implicit casting does not  
work for template parameters, in other words, TmpI!TmpC2 does not  
implicitly cast to TmpI!TmpC.

-Steve
May 06 2011
parent reply Jason House <jason.james.house gmail.com> writes:
Steven Schveighoffer Wrote:


 On Fri, 06 May 2011 03:39:31 -0400, Mariusz Gliwiński  
 <alienballance gmail.com> wrote:
 

 Is this bug, or is it as supposed to be? I'm not sure...
 <code>
 interface TmpI(T) {
      void func(T);
 }

 class TmpC {}
 class TmpC2 : TmpC {}

 class Tmp : TmpI!TmpC2 {
      void func(TmpI!TmpC) {};


 
 Here is one problem, TmpI is instantiated with TmpC2 as the func  
 parameter, yet you use TmpI!TmpC as your func parameter.  The func  
 parameter should be TmpC2.  I'm surprised this part would compile without  
 complaining that you didn't implement func.  But it probably would fail if  
 it got to that check.



This part is fine. When extending a class or interface, you are free to widen
the input and narrow the output. Users of the interface can pass in TmpC2 (it's
a valid TmpC)
May 06 2011
parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Fri, 06 May 2011 08:49:44 -0400, Jason House  
<jason.james.house gmail.com> wrote:


 Steven Schveighoffer Wrote:


 On Fri, 06 May 2011 03:39:31 -0400, Mariusz Gliwiński
 <alienballance gmail.com> wrote:


 Is this bug, or is it as supposed to be? I'm not sure...
 <code>
 interface TmpI(T) {
      void func(T);
 }

 class TmpC {}
 class TmpC2 : TmpC {}

 class Tmp : TmpI!TmpC2 {
      void func(TmpI!TmpC) {};


 Here is one problem, TmpI is instantiated with TmpC2 as the func
 parameter, yet you use TmpI!TmpC as your func parameter.  The func
 parameter should be TmpC2.  I'm surprised this part would compile  
 without
 complaining that you didn't implement func.  But it probably would fail  
 if
 it got to that check.



 This part is fine. When extending a class or interface, you are free to  
 widen the input and narrow the output. Users of the interface can pass  
 in TmpC2 (it's a valid TmpC)


But look at TmpI, if T is TmpC2, then func's param is TmpC2.  This can't  
be implemented with TmpI!TmpC.

Let's take templates out of it, and look at what is generated:

interface TmpI1 // in original exmample, this is TmpI!TmpC2
{
    void func(TmpC2);
}

interface TmpI2 // in original example, this is TmpI!TmpC
{
    void func(TmpC);
}

class Tmp : TmpI1
{
    void func(TmpI2) {}
}

There is no way TmpI2 casts implicitly to or from TmpC2, they are  
unrelated types.

-Steve
May 06 2011