• dsimcha (25/25) Oct 28 2010 I've just found a new D-specific design pattern for simulating non-virtu...
• Simen kjaeraas (4/22) Oct 28 2010 I believe this is mentioned in TDPL.
• Jimmy Cao (2/2) Oct 28 2010 Well, you can't have multiple alias this's right?
• Simen kjaeraas (23/25) Oct 28 2010 It is extensible like this:
• Simen kjaeraas (5/6) Oct 28 2010 Problem is of course, no reliable way to hijack
• Jesse Phillips (2/8) Oct 28 2010 This is an issue with the implementation, the language allows for as man...
• Jonathan M Davis (5/15) Oct 28 2010 Yeah. TDPL specifically says that you can have multiple alias this's (in...
• tls (2/17) Oct 29 2010 So no D2 staple for me ? When is ready? TDLP not high priority?

dsimcha <dsimcha yahoo.com> writes:

I've just found a new D-specific design pattern for simulating non-virtual
multiple inheritance by abusing inner classes and alias this.  Here's an
example:

class Foo {
    uint num = 2;
}

class Bar {
    uint num = 3;
}

class Outer : Foo {

    class Inner : Bar {}

    Inner inner;

    this() {
        inner = new Inner;
    }

    alias inner this;
}

Basically, this satisfies all of the requirements for simulated multiple
inheritance:

1.  An Outer can be implicitly converted to either a Foo or a Bar.

2.  It obtains both interface and implementation from both Foo and Bar.

3.  The methods of Outer that override stuff from Foo have access to
Bar-related stuff and vice-versa.

Should this be listed somewhere as D's answer to lack of multiple inheritance?
 I find it very cool that the language is expressive enough to reasonably
simulate MI.

"Simen kjaeraas" <simen.kjaras gmail.com> writes:

dsimcha <dsimcha yahoo.com> wrote:

 I've just found a new D-specific design pattern for simulating  
 non-virtual
 multiple inheritance by abusing inner classes and alias this.  Here's an  
 example:

 class Foo {
     uint num = 2;
 }

 class Bar {
     uint num = 3;
 }

 class Outer : Foo {

     class Inner : Bar {}

     Inner inner;

     this() {
         inner = new Inner;
     }

     alias inner this;
 }

I believe this is mentioned in TDPL.

-- 
Simen

Jimmy Cao <jcao219 gmail.com> writes:

Well, you can't have multiple alias this's right?

So then, wouldn't it still only limit to 2 base classes?

"Simen kjaeraas" <simen.kjaras gmail.com> writes:

Jimmy Cao <jcao219 gmail.com> wrote:

 Well, you can't have multiple alias this's right?

 So then, wouldn't it still only limit to 2 base classes?

It is extensible like this:

class Outer : Foo {
     class Inner : Bar {
         class InnerInner : Baz {
         }

         InnerInner innerInner;
		
         this() {
             innerInner = new InnerInner;
         }
		
         alias innerInner this;
     }

     Inner inner;

     this() {
         inner = new Inner;
     }

     alias inner this;
}

It should be possible to turn this into a mixin.


-- 
Simen

"Simen kjaeraas" <simen.kjaras gmail.com> writes:

Simen kjaeraas <simen.kjaras gmail.com> wrote:

 It should be possible to turn this into a mixin.

Problem is of course, no reliable way to hijack
constructors to initialize the inner class.

-- 
Simen

Jesse Phillips <jessekphillips+D gmail.com> writes:

Jimmy Cao Wrote:

 Well, you can't have multiple alias this's right?
 
 So then, wouldn't it still only limit to 2 base classes?
 
 Well, you can't have multiple alias this's right?<div><br></div><div>So then,
wouldn't it still only limit to 2 base classes?</div>
 

This is an issue with the implementation, the language allows for as many alias
this as you wish.

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Thursday, October 28, 2010 15:46:23 Jesse Phillips wrote:
 Jimmy Cao Wrote:
 Well, you can't have multiple alias this's right?
 
 So then, wouldn't it still only limit to 2 base classes?
 
 Well, you can't have multiple alias this's right?<div><br></div><div>So
 then, wouldn't it still only limit to 2 base classes?</div>

 
 This is an issue with the implementation, the language allows for as many
 alias this as you wish.

Yeah. TDPL specifically says that you can have multiple alias this's (in the 
section on this exact topic too, IIRC), so it's on the list of things that TDPL 
says and D that dmd hasn't correctly implemented yet.

- Jonathan M Davis

tls <do notha.ev> writes:

Jonathan M Davis Wrote:

 On Thursday, October 28, 2010 15:46:23 Jesse Phillips wrote:
 Jimmy Cao Wrote:
 Well, you can't have multiple alias this's right?
 
 So then, wouldn't it still only limit to 2 base classes?
 
 Well, you can't have multiple alias this's right?<div><br></div><div>So
 then, wouldn't it still only limit to 2 base classes?</div>

 
 This is an issue with the implementation, the language allows for as many
 alias this as you wish.

 
 Yeah. TDPL specifically says that you can have multiple alias this's (in the 
 section on this exact topic too, IIRC), so it's on the list of things that
TDPL 
 says and D that dmd hasn't correctly implemented yet.

So no D2 staple for me ? When is ready? TDLP not high priority?