www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Non-Virtual Interfaces

reply =?UTF-8?B?QWxla3NhbmRhciBSdcW+acSNacSH?= <ruzicic.aleksandar gmail.com> writes:
I'm trying to use NVI idiom but i keep getting errors from dmd.

This is my setup:

module test;

import std.stdio;

interface IBase {
	void foo();
	void bar();
}

interface IBar : IBase {
	final void bar() {
		writefln("IBar.bar()");
	}
}

class Foo : IBar {

	void foo() {
		writefln("Foo.foo()");
	}
}

void main() {

	Foo foo = new Foo();
	foo.foo();
}

When I try to compile it i get "test.d(16): Error: class test.Foo
interface function IBar.bar isn't implemented"

And if I try to define bar() in Foo i receive "test.d(22): Error:
function test.Foo.bar cannot override final function
IBar.test.IBar.bar"
which is expected since IBar.bar() is final.

So, am I missing some point about NVIs here or is it just not yet
implemented in dmd?
Mar 04 2011
next sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Fri, 04 Mar 2011 05:17:00 -0500, Aleksandar Ružičić  
<ruzicic.aleksandar gmail.com> wrote:

 I'm trying to use NVI idiom but i keep getting errors from dmd.

 This is my setup:

 module test;

 import std.stdio;

 interface IBase {
 	void foo();
 	void bar();
 }

 interface IBar : IBase {
 	final void bar() {
 		writefln("IBar.bar()");
 	}
 }

 class Foo : IBar {

 	void foo() {
 		writefln("Foo.foo()");
 	}
 }

 void main() {

 	Foo foo = new Foo();
 	foo.foo();
 }

 When I try to compile it i get "test.d(16): Error: class test.Foo
 interface function IBar.bar isn't implemented"

 And if I try to define bar() in Foo i receive "test.d(22): Error:
 function test.Foo.bar cannot override final function
 IBar.test.IBar.bar"
 which is expected since IBar.bar() is final.

 So, am I missing some point about NVIs here or is it just not yet
 implemented in dmd?

The traditional explanation of NVI is that the final function is never virtual. In your case, bar must be virtual at the IBase level, so it must go in the vtable. I'm unsure whether this is intended to be a bug or a feature. What you may want to consider is an abstract class instead of NVI, as long as you don't need multiple inheritance, it should be fine. -Steve
Mar 04 2011
prev sibling parent =?UTF-8?B?QWxla3NhbmRhciBSdcW+acSNacSH?= <ruzicic.aleksandar gmail.com> writes:
 What you may want to consider is an abstract class instead of NVI, as long
 as you don't need multiple inheritance, it should be fine.

 -Steve

Well, I've decided to give NVI a try just because multiple inheritance would be best way to do what I want (aldo I hate that feature of C++ and just don't use it) but it seems I can't do it with a NVI either... So back to the drawing board for me :) thanks for reply - Aleksandar
Mar 04 2011