Multiple class inheritance

[Robert Fraser]

Heinz wrote:
> Hi,
> 
> Is it posible to do multiple class inheritance in D?
> 
> Example:
> 
> class A
> {
> 
> }
> 
> class B
> {
> 
> }
> 
> class C : A, B
> {
> 
> }
> 
> Am i dreaming or it can be done?

The way something like this is generally done is by using interfaces.

In the _rare_ case I need true MI (that is, with implementations), I 
tend to make one or both of the classes an interface with a "standard 
implementation" template. So something like:

class A
{
     void foo()
     {
         writefln("A.foo");
     }
}

interface B
{
     void bar();

     template B_Impl()
     {
         void bar()
         {
             writefln("B.bar");
         }
     }
}

class C : A, B
{
     mixin B.B_Impl!();
}

class D : A, B
{
     override void foo()
     {
         writefln("D.foo");
     }

     override void bar()
     {
         writefln("D.bar");
     }
}

int main(char[][] args)
{
     A a = new A();
     C c = new C();
     D d = new D();

     A a_c = c;
     A a_d = d;
     B b_c = c;
     B b_d = d;

     a.foo();    // A.foo
     c.foo();    // A.foo
     d.foo();    // D.foo
     a_c.foo();  // A.foo
     a_d.foo();  // D.foo

     c.bar();    // B.bar
     d.bar();    // D.bar
     b_c.bar();  // B.bar
     b_d.bar();  // D.bar

     return 0;
}

You might want to give every interface-with-implementation an init() 
method, too, to call during construction, and of course be wary of name 
clashes and deep inheritance hierarchies are a lot more difficult to 
manage, but, hey, there's no diamond problem.