Q: How to return sub class from base class method

[Myron Alexander]

Jari-Matti Mäkelä wrote:
> Kirk McDonald wrote:
> 
>> Jari-Matti Mäkelä wrote:
>>> class A(T) {
>>>   T doSomething() {
>>>     ...
>>>     return cast(T)this;
>>>   }
>>> }
>>>
>>> class B(T) : A!(T) {
>>>   T doSomethingElse() {
>>>     ...
>>>     return cast(T)this;
>>>   }
>>> }
>>>
>>> There might be other (more clever) ways to do this too. Like a mixin for
>>> the "selftype" or something.
>> I believe B should look like this, if you're using that pattern:
>>
>> class B : A!(B) {
>>    B doSomethingElse() {
>>      // ...
>>      return this;
>>    }
>> }
> 
> Actually no - class B was supposed to be in the middle of the hierarchy so
> class C would have looked like that :)
> 
> Something like
> 
> class A(T = A) { ... }
> class B(T = B) : A!(T) { ... }
> 
> would have been nice for those non-abstract base classes so they could have
> been instantiated too, but apparently the compiler didn't want to
> co-operate this time.
> 
>> Thus, B is derived from a class template to which you pass B as a
>> parameter. This is often used in C++ as a way of emulating mixin-like
>> behavior. Thus, D's template mixins could very well be a better solution.
>>
> 
> Feel free to create a better solution :)

Thanks all.

I am happy with the mixin solution, even if I forget to add the mixin, 
the compiler will generate an error when I try to chain the class 
methods after the doSomething so it's not a dangerous one at that.

Just for your information, I attached the test source where I am using 
it. The doSomething method here is called 'initCause'.

Regards,

Myron.

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