From: Rajinder Yadav <devguy.ca@...>
Date: 2010-11-01T07:54:22+09:00
Subject: Re: the dark side of inherited methods

On 10-10-31 06:42 PM, Phillip Gawlowski wrote:
> On Sun, Oct 31, 2010 at 11:30 PM, timr<timrandg@gmail.com>  wrote:
>> I noticed that I inherited the Array#collect and Array#collect!
>> methods. Yeah for inheritance! But then look at the returned classes.
>> Array#collect returns and array. Array.collect! returns a Vector. If
>> you look at the underlying C code that defines these methods the
>> response makes sense. Collect! alters the object itself using the
>> results from the block, while collect builds a new Array from the
>> results of the block. But geesh, that means to have consistent
>> behavior, I have to add the following (and worse, look through every
>> other Array method to determine if the return value should be a vector
>> rather than an array):
>
> Define "consistent behavior". That #collect returns an Array is
> consistent with other, similar language constructs. The question is if
> you want an Array back, or want a Vector back from the operation you
> perform. Similarly, since you inherited the Array methods, Vector#join
> will behave exactly like Array#join.
>
> That's pretty much the point of inheritance: Re-using a class's
> methods to make your own life easier by reducing the work you need to
> do, since most methods you expect to use are identical to what you
> need, and only need adaptation to your own needs (via encapsulation,
> or overriding, for example).
>
> Maybe you have better success (i.e. less work), if you a) encapsulate
> similar calls into calls of your own and massage the operation that
> way, or b) you move one up in the inheritance change, and use
> Enumerable to inherit from. Most work will be c) create your class
> from scratch, and mix in Array or Enumerable.
>
> TL;DR: Any class derived from another class will inherit its method.
> That's true for Ruby, as it is for Java or C#. It's pretty much the
> point of inheritance. ;)
>

I see how Vector is-a Array, I don't see how Array is-a Vector? I would 
consider collect and collect! to be inconsistent under this definition.

-- 
Kind Regards,
Rajinder Yadav | DevMentor.org | Do Good! ~ Share Freely

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