Real Problems with Python

[William Tanksley]

On 15 Feb 2000 01:27:32 GMT, Neel Krishnaswami wrote:
>Justus Pendleton <justus at my-deja.com> wrote:
>>   neelk at alum.mit.edu wrote:
>> > > > 3. Multiple inheritance is unsound

>> > > >  By 'unsound' I mean that a method call to a method inherited by
>> > > >  a subclass of two other classes can fail, even if that method
>> > > >  call would work on an instance of the base class.

>So I looked at some other dynamic languages to see what they did.

>o Dylan -- forbids using MI when there are multiple slots with the 
>  same name.

>Other languages seem to either forbid name conflicts or just suck it
>up and live with an unsafe rule, which leads me to conclude that the
>moral is TANSTAAFL -- there ain't no such thing as a free lunch.

Sather uses yet another system, which I see as very interesting -- it
totally disallows inheritance of every kind (single AND multiple).  In its
place it offers two concepts: interface and importation.

Let me give a pseudo-Python example:

# the base class
class First:
  def fun(hmm):
    print hmm

# this is how to exactly imitate Python's current
# behavior (assuming no extra error checks occur)
class Second(First):
  import First

# here we 'subclass' from First, but we don't inherit _any_
# behavior or data.
class Third(First):
  def fun(yadda):
    print "Whee!", yadda

# Here the compiler will print an error message, because we don't define
# any implementation of the interface we claim.
class Fourth(First):
  def boring():
    print "braces are cool, indentation sucks!"

This is only a single-inheritance example, of course.  The rest is left as
an excercise to the reader.

>Neel

-- 
-William "Billy" Tanksley, in hoc signo hack