• Janice Caron (13/13) Sep 12 2007 Will alias this work for classes too?
• davidl (5/18) Sep 12 2007 Ah, I haven't noticed such brilliant!
• Jascha Wetzel (3/20) Sep 13 2007 that would be a different syntax for regular MI and is therefore
• Janice Caron (7/9) Sep 13 2007 "alias this" is already slated in in the Walter Andrei document.
• Jascha Wetzel (6/17) Sep 13 2007 that depends on what you want to do on name collisions. structs don't
• Sean Kelly (8/18) Sep 13 2007 If I had to guess, I'd say "alias this" will basically perform a mix-in
• Jascha Wetzel (25/37) Sep 13 2007 mixin merely copies declarations at compile-time. "alias b this" in the

"Janice Caron" <caron800 googlemail.com> writes:

Will alias this work for classes too?

An in,

class A { int a; }
class B { int b; }
class C { int c; }

class X : A
{
    B b;
    C c;
    alias b this;
    alias c this;
}

Fake multiple inheritance!

davidl <davidl 126.com> writes:

Ah, I haven't noticed such brilliant!

在 Thu, 13 Sep 2007 06:08:48 +0800，Janice Caron <caron800 googlemail.com>  
写道:

 Will alias this work for classes too?

 An in,

 class A { int a; }
 class B { int b; }
 class C { int c; }

 class X : A
 {
     B b;
     C c;
     alias b this;
     alias c this;
 }

 Fake multiple inheritance!



-- 
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Jascha Wetzel <"[firstname]" mainia.de> writes:

Janice Caron wrote:
 Will alias this work for classes too?
 
 An in,
 
 class A { int a; }
 class B { int b; }
 class C { int c; }
 
 class X : A
 {
     B b;
     C c;
     alias b this;
     alias c this;
 }
 
 Fake multiple inheritance!

that would be a different syntax for regular MI and is therefore 
probably not going to happen.

"Janice Caron" <caron800 googlemail.com> writes:

On 9/13/07, Jascha Wetzel <"[firstname]" mainia.de> wrote:
 that would be a different syntax for regular MI and is therefore
 probably not going to happen.

"alias this" is already slated in in the Walter Andrei document.
Walter apparently /wants/ "alias this", and it looks like it will work
as I outlined - at least for structs. Classes? I don't know. That's
why I asked.

It's not real multiple inheritance. Nobody should pretend it is. But
it does "fake it" to a certain extent..

Jascha Wetzel <"[firstname]" mainia.de> writes:

Janice Caron wrote:
 On 9/13/07, Jascha Wetzel <"[firstname]" mainia.de> wrote:
 that would be a different syntax for regular MI and is therefore
 probably not going to happen.

 
 "alias this" is already slated in in the Walter Andrei document.
 Walter apparently /wants/ "alias this", and it looks like it will work
 as I outlined - at least for structs. Classes? I don't know. That's
 why I asked.
 
 It's not real multiple inheritance. Nobody should pretend it is. But
 it does "fake it" to a certain extent..

that depends on what you want to do on name collisions. structs don't 
have inheritance or virtual functions, which greatly simplifies the 
problem. once you deal with inheritance and virtual functions as 
intuitively expected (at least as I intuitively expected), it'll be like 
real MI.

Sean Kelly <sean f4.ca> writes:

Janice Caron wrote:
 On 9/13/07, Jascha Wetzel <"[firstname]" mainia.de> wrote:
 that would be a different syntax for regular MI and is therefore
 probably not going to happen.

 
 "alias this" is already slated in in the Walter Andrei document.
 Walter apparently /wants/ "alias this", and it looks like it will work
 as I outlined - at least for structs. Classes? I don't know. That's
 why I asked.

If I had to guess, I'd say "alias this" will basically perform a mix-in 
of the data.  So I don't see any reason why it couldn't work for classes.

 It's not real multiple inheritance. Nobody should pretend it is. But
 it does "fake it" to a certain extent..

See this link for an example of mixin multiple inheritance:

http://www.invisibleduck.org/~sean/code/io/stream.d

It's not an approach I'd want to use regularly, but it can come in handy 
for eliminating code duplication in some instances.


Sean

Jascha Wetzel <"[firstname]" mainia.de> writes:

Sean Kelly wrote:
 Janice Caron wrote:
 On 9/13/07, Jascha Wetzel <"[firstname]" mainia.de> wrote:
 that would be a different syntax for regular MI and is therefore
 probably not going to happen.

 "alias this" is already slated in in the Walter Andrei document.
 Walter apparently /wants/ "alias this", and it looks like it will work
 as I outlined - at least for structs. Classes? I don't know. That's
 why I asked.

 
 If I had to guess, I'd say "alias this" will basically perform a mix-in 
 of the data.  So I don't see any reason why it couldn't work for classes.

mixin merely copies declarations at compile-time. "alias b this" in the 
sense of the version from Walter's and Andrei's slides, would have to 
use the reference to the aggregated object to access it's members.
a couple of issues come to mind:

- while a method that has been mixed in can be overridden in a subclass, 
a method that has been imported via alias-this can't (unless alias-this 
would change the vtable of the importing class, which would lead to real 
MI).

- consider this:

class A { void foo(int); }
class B { void foo(int); }
class C : A { override void foo(int); }
class D : B
{
   C c;
   alias C this;
}

what is D.foo?

- the diamond problem of MI also arises

- accessing a member (even if it's of primitive type) can result in an 
access violation although the reference used by the caller is non-null - 
the aggregated object might be null.

sure, these issues can be overcome, but it appears similarly complex as 
real MI to me.