[E-Lang] Re: inheritance, delegation, mental models for beginners

[zooko@zooko.com]

 MarkM wrote:

> Hi guys, I'm not sure what you're each saying here.  I think we all agree on 
> the meaning of "delegation" by itself:  A delegates to B is A forwards all 
> messages it doesn't directly understand to B.  This is represented directly 
> in E as
> 
>     def A {
>         to ... { ... }
>         to ... { ... }
>         ...
>         delegate { B }
>     }
> 
> There is no implication that B even has a reference to A, much less that it 
> invokes A to give it a change to override behavior defined by B.
> 
> Chip, I believe you're saying that we should simply stop here and say "this 
> is inheritance".  Dean, I think you think you're agreeing with Chip, but I'm 
> not at all sure you'd agree with what I think Chip is saying (whether Chip 
> is actually saying it or not.  Chip?)
> 
> The Treaty of Orlando, as well as the inheritance you designed for Vulcan, 
> I'll call "dynamic inheritance" to distinguish it from E's "static 
> inheritance".  However, both are built as a pattern of delegation involving 
> multiple simple delegations, and both have B give A a chance to override 
> default behaviors in B.  This is indeed "inheritance *by* delegation", as 
> opposed to what I take Chip to be saying, which is "inheritance is delegation".


Whoops -- I see that `dynamic inheritance' is already taken (as I should have
realized from _tToO_).  Darn.

I understand that `inheritance' is the wrong word for this feature, but based on my
reading of "The Treaty of Orlando", `delegation' is equally a wrong word.

(I realize that the dynamic, explicit, and fine-grained nature of E `delegation'
makes it have more in common with _tToO_ `delegation' than with _tToO_
`inheritance', but along the axis of encapsulation vs. extension of the
superclass, it is neither _tToO_'s `inheritance' nor `delegation'.)


How about "Encapsulated Inheritance" or "Safe Inheritance"?


You could, for example, provide different keywords like `extend' and `reuse'
instead of `inherit' and `delegate', and describe both of them as inheritance, and
the first as "extension inheritance" and the second as "safe inheritance".


Regards,

Zooko