digitalmars.D.learn - interface and class inheritance

Oleg B (22/22) Nov 14 2013 [code]

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (23/45) Nov 14 2013 One way is to expose B through 'alias this' (not by inheritance) but it
Agustin (9/32) Nov 14 2013 Try

Agustin (10/49) Nov 14 2013 Oh sorry i mean

Oleg B (2/54) Nov 14 2013 we can't change anything in class B

Jacob Carlborg (5/18) Nov 15 2013 I would have moved "final void funcA()" to a template and mixin it in

Chris Nicholson-Sauls (11/11) Nov 17 2013 I had thought the pattern
Stretto (11/34) Nov 17 2013 This is ambiguous. In one case, from A, you are allowing

"Oleg B" <code.viator gmail.com> writes:

[code]
import std.stdio;

interface A { void funcA(); }
class B { final void funcA() { writeln( "B.funcA()" ); } }

class C: B, A { }

void main()
{
     auto c = new C;
     c.funcA();
}
[code/]

$ dmd -run interface.d
interface.d(6): Error: class interface.C interface function 'void 
funcA()' is not implemented

if swap A and B
[code]
class C: A, B { }
[code/]

$ dmd -run interface.d
interface.d(6): Error: class interface.C base type must be 
interface, not interface.B

how to workaround this without change in class B and interface A?

Nov 14 2013

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 11/14/2013 01:20 PM, Oleg B wrote:
 [code]
 import std.stdio;

 interface A { void funcA(); }
 class B { final void funcA() { writeln( "B.funcA()" ); } }

 class C: B, A { }

 void main()
 {
      auto c = new C;
      c.funcA();
 }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C interface function 'void
 funcA()' is not implemented

 if swap A and B
 [code]
 class C: A, B { }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C base type must be interface,
 not interface.B

 how to workaround this without change in class B and interface A?

One way is to expose B through 'alias this' (not by inheritance) but it 
doesn't scale because currently only one 'alias this' is allowed.

import std.stdio;

interface A { void funcA(); }
class B { final void funcA() { writeln( "B.funcA()" ); } }

class C: A {
     B b;
     alias b this;

     this(){
         b = new B();
     }

     void funcA()
     {
         return b.funcA();
     }
}

void main()
{
     auto c = new C;
     c.funcA();
}

Ali

Nov 14 2013

"Agustin" <agustin.l.alvarez hotmail.com> writes:

On Thursday, 14 November 2013 at 21:20:57 UTC, Oleg B wrote:
 [code]
 import std.stdio;

 interface A { void funcA(); }
 class B { final void funcA() { writeln( "B.funcA()" ); } }

 class C: B, A { }

 void main()
 {
     auto c = new C;
     c.funcA();
 }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C interface function 
 'void funcA()' is not implemented

 if swap A and B
 [code]
 class C: A, B { }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C base type must be 
 interface, not interface.B

 how to workaround this without change in class B and interface 
 A?

Try

interface A {
   final void funcA();
}
class B {
   final void funcA() { writeln( "B.funcA()" ); }
}

class C: B, A { }

Nov 14 2013

"Agustin" <agustin.l.alvarez hotmail.com> writes:

On Thursday, 14 November 2013 at 21:42:38 UTC, Agustin wrote:
 On Thursday, 14 November 2013 at 21:20:57 UTC, Oleg B wrote:
 [code]
 import std.stdio;

 interface A { void funcA(); }
 class B { final void funcA() { writeln( "B.funcA()" ); } }

 class C: B, A { }

 void main()
 {
    auto c = new C;
    c.funcA();
 }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C interface function 
 'void funcA()' is not implemented

 if swap A and B
 [code]
 class C: A, B { }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C base type must be 
 interface, not interface.B

 how to workaround this without change in class B and interface 
 A?

 Try

 interface A {
   final void funcA();
 }
 class B {
   final void funcA() { writeln( "B.funcA()" ); }
 }

 class C: B, A { }

Oh sorry i mean

interface A {
   void funcA();
}

class B : A {
   final void funcA() { writeln( "B.funcA()" ); }
}

class C : B {
}

Nov 14 2013

"Oleg B" <code.viator gmail.com> writes:

On Thursday, 14 November 2013 at 21:45:11 UTC, Agustin wrote:
 On Thursday, 14 November 2013 at 21:42:38 UTC, Agustin wrote:
 On Thursday, 14 November 2013 at 21:20:57 UTC, Oleg B wrote:
 [code]
 import std.stdio;

 interface A { void funcA(); }
 class B { final void funcA() { writeln( "B.funcA()" ); } }

 class C: B, A { }

 void main()
 {
   auto c = new C;
   c.funcA();
 }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C interface function 
 'void funcA()' is not implemented

 if swap A and B
 [code]
 class C: A, B { }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C base type must be 
 interface, not interface.B

 how to workaround this without change in class B and 
 interface A?

 Try

 interface A {
  final void funcA();
 }
 class B {
  final void funcA() { writeln( "B.funcA()" ); }
 }

 class C: B, A { }

 Oh sorry i mean

 interface A {
   void funcA();
 }

 class B : A {
   final void funcA() { writeln( "B.funcA()" ); }
 }

 class C : B {
 }

we can't change anything in class B

Nov 14 2013

Jacob Carlborg <doob me.com> writes:

On 2013-11-14 23:17, Oleg B wrote:

 Oh sorry i mean

 interface A {
   void funcA();
 }

 class B : A {
   final void funcA() { writeln( "B.funcA()" ); }
 }

 class C : B {
 }

 we can't change anything in class B

I would have moved "final void funcA()" to a template and mixin it in 
both B and C, but if you cannot change B that won't work.

-- 
/Jacob Carlborg

Nov 15 2013

"Chris Nicholson-Sauls" <ibisbasenji gmail.com> writes:

I had thought the pattern

     alias B.funcA funcA;

was supposed to solve things like this, but it does not work.  
Any reason it couldn't be made to?  Or, for that matter, why 
inherited members are not considered by interfaces in the first 
place?

In related news, if you simply leave A out of C's declaration, 
then do something like:

     A a = cast(A) c;
     a.funcA();

you will get a segfault.  Hooray.

Nov 17 2013

"Stretto" <uiy12345 gmail.com> writes:

On Thursday, 14 November 2013 at 21:20:57 UTC, Oleg B wrote:
 [code]
 import std.stdio;

 interface A { void funcA(); }
 class B { final void funcA() { writeln( "B.funcA()" ); } }

 class C: B, A { }

 void main()
 {
     auto c = new C;
     c.funcA();
 }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C interface function 
 'void funcA()' is not implemented

 if swap A and B
 [code]
 class C: A, B { }
 [code/]

 $ dmd -run interface.d
 interface.d(6): Error: class interface.C base type must be 
 interface, not interface.B

 how to workaround this without change in class B and interface 
 A?

This is ambiguous. In one case, from A, you are allowing 
inheritance and in B you are preventing it.

c.funcA will call the interface version unless you cast to B.

But it should be an easy fix

class C : B, A
{
     void funcA() { ((cast(B))this).funcA(); }
}

This simply redirects funcA(in C, but using interface A) to funcA 
in B, which is final.

Nov 17 2013

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digitalmars.D.learn - interface and class inheritance