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digitalmars.D - Are interfaces supported in Better C mode?

reply Dibyendu Majumdar <d.majumdar gmail.com> writes:
Reading the docs on Better C mode I got the impression that it 
should be possible to implement an interface in a struct. Is this 
not the case?

I tried extern (C++) too, but I get an error.

extern (C++) interface A {
     void sayHello();
}

extern (C++) struct B : A {

}
Nov 14 2020
next sibling parent reply Dibyendu Majumdar <d.majumdar gmail.com> writes:
On Saturday, 14 November 2020 at 21:09:59 UTC, Dibyendu Majumdar 
wrote:

 Reading the docs on Better C mode I got the impression that it 
 should be possible to implement an interface in a struct. Is 
 this not the case?


I guess it needs to be class?

extern (C++) interface A {
     void sayHello();
}

extern (C++) class B : A {

     void sayHello() {}

}

Above seems to compile.
Nov 14 2020
parent reply Dibyendu Majumdar <d.majumdar gmail.com> writes:
On Saturday, 14 November 2020 at 21:40:31 UTC, Dibyendu Majumdar 
wrote:

 On Saturday, 14 November 2020 at 21:09:59 UTC, Dibyendu 
 Majumdar wrote:

 Reading the docs on Better C mode I got the impression that it 
 should be possible to implement an interface in a struct. Is 
 this not the case?


 I guess it needs to be class?


Well this compiles but doesn't link.

import core.stdc.stdio : printf;

extern (C++) interface A {
     void sayHello();
}

extern (C++) class B : A {

     void sayHello() {
         printf("hello\n");
     }
}

extern (C) void main() {
     B b;
     b.sayHello();
}


/opt/rh/devtoolset-9/root/usr/libexec/gcc/x86_64-redhat-linux/9/ld:
interfaces.o:(.data._D10interfaces1A11__InterfaceZ+0x0): undefined reference to
`_D14TypeInfo_Class6__vtblZ'
/opt/rh/devtoolset-9/root/usr/libexec/gcc/x86_64-redhat-linux/9/ld:
interfaces.o:(.data._D10interfaces1B6__initZ+0x8): undefined reference to
`_D10interfaces1B7__ClassZ'
Nov 14 2020
parent reply kinke <noone nowhere.com> writes:
On Saturday, 14 November 2020 at 21:46:38 UTC, Dibyendu Majumdar 
wrote:

 Well this compiles but doesn't link.


This works with LDC:

import core.stdc.stdio : printf;

extern (C++) interface A {
     void sayHello();
}

extern (C++) class B : A {
     void sayHello() {
         printf("hello\n");
     }
}

extern (C) void main() {
     scope b = new B;
     b.sayHello();
}
Nov 14 2020
next sibling parent Dibyendu Majumdar <d.majumdar gmail.com> writes:
On Sunday, 15 November 2020 at 01:00:27 UTC, kinke wrote:

 On Saturday, 14 November 2020 at 21:46:38 UTC, Dibyendu 
 Majumdar wrote:

 Well this compiles but doesn't link.


 This works with LDC:

 import core.stdc.stdio : printf;

 extern (C++) interface A {
     void sayHello();
 }

 extern (C++) class B : A {
     void sayHello() {
         printf("hello\n");
     }
 }

 extern (C) void main() {
     scope b = new B;
     b.sayHello();
 }


Hi,

I downloaded ldc2 1.24 and tried this out.
It compiled and linked okay - but crashes with segmentation fault 
on the line that invokes the sayHello() method.

I am on RHEL 7.9.

Regards
Nov 14 2020
prev sibling parent reply Dibyendu Majumdar <d.majumdar gmail.com> writes:
On Sunday, 15 November 2020 at 01:00:27 UTC, kinke wrote:

 On Saturday, 14 November 2020 at 21:46:38 UTC, Dibyendu 
 Majumdar wrote:

 Well this compiles but doesn't link.


 This works with LDC:

 extern (C) void main() {
     scope b = new B;
     b.sayHello();
 }


I thought new isn't supported in better C mode ?
Nov 14 2020
parent reply Paul Backus <snarwin gmail.com> writes:
On Sunday, 15 November 2020 at 01:30:24 UTC, Dibyendu Majumdar 
wrote:

 On Sunday, 15 November 2020 at 01:00:27 UTC, kinke wrote:

 On Saturday, 14 November 2020 at 21:46:38 UTC, Dibyendu 
 Majumdar wrote:

 Well this compiles but doesn't link.


 This works with LDC:

 extern (C) void main() {
     scope b = new B;
     b.sayHello();
 }


 I thought new isn't supported in better C mode ?


`scope` causes the class instance to be allocated on the stack.

Source: https://dlang.org/spec/expression.html#new_expressions
Nov 14 2020
parent Dibyendu Majumdar <d.majumdar gmail.com> writes:
On Sunday, 15 November 2020 at 01:43:00 UTC, Paul Backus wrote:

 On Sunday, 15 November 2020 at 01:30:24 UTC, Dibyendu Majumdar



 I thought new isn't supported in better C mode ?


 `scope` causes the class instance to be allocated on the stack.

 Source: https://dlang.org/spec/expression.html#new_expressions


Okay thank you - I didn't know that.
Nov 14 2020
prev sibling parent reply Dibyendu Majumdar <mobile majumdar.org.uk> writes:
On Saturday, 14 November 2020 at 21:09:59 UTC, Dibyendu Majumdar 
wrote:

 Reading the docs on Better C mode I got the impression that it 
 should be possible to implement an interface in a struct. Is 
 this not the case?


https://issues.dlang.org/show_bug.cgi?id=21412
Nov 21 2020
parent Dibyendu Majumdar <mobile majumdar.org.uk> writes:
On Saturday, 21 November 2020 at 23:48:06 UTC, Dibyendu Majumdar 
wrote:

 On Saturday, 14 November 2020 at 21:09:59 UTC, Dibyendu 
 Majumdar wrote:

 Reading the docs on Better C mode I got the impression that it 
 should be possible to implement an interface in a struct. Is 
 this not the case?


 https://issues.dlang.org/show_bug.cgi?id=21412


Looks like this works with DMD and LDC:

import core.stdc.stdio : printf;

extern (C++) abstract class A {
     void sayHello();
}

extern (C++) class B : A {
     override void sayHello() {
         printf("hello\n");
     }
}

extern (C) void main() {
     scope b = new B;
     b.sayHello();
}

So - replacing 'interface' with 'abstract class' solved it.
Also need to use 'new' to allocate. Compiler doesn't complain 
about the null value.
Nov 21 2020