From: Guillaume Marcais <guslist@...>
Date: 2004-04-04T21:28:55+09:00
Subject: Re: deciding between ruby and python

Le 4 avr. 04, � 05:37, Dan Doel a �crit :
> Actually, in a sense, the automatic conversion is duck typing in this 
> case.
> Defining #to_s in a Ruby class means, "You should call this to 
> automatically
> convert if a String is expected."  If you just want to be able to cast 
> to a
> String, you define #to_str. This is not called for implicit 
> conversion, and is
> more analogous to the __str__ method in Python, I think.  The only 
> difference
> is that Object has a default #to_s, so if you want it to raise an 
> exception,
> you need to redefine it to do so.
>
> At least, that's how I've seen it described (and a quick check reveals 
> that
> join calls #to_s, never #to_str, and when I redefine #to_s, it can 
> throw an
> exception, just like Python would).

I had the exact opposite understanding of the meaning of #to_s and 
#to_str.

$ cat str.rb
class Toto; end
t = Toto.new

begin
   puts("hello " + t)
rescue Exception => e
   puts("Error " + e.message)
end

class Toto
   def to_str
     "toto"
   end
end

begin
   puts("hello " + t)
rescue Exception => e
   puts("Error " + e.message)
end

$ ruby str.rb
Error cannot convert Toto into String
hello toto

#join on the other hand calls #to_s on each element of the Array.

Guillaume.

>> Aren't you blowing this out of proportion? Would Python be on the
>> 'wild side' if it added the following function:
>>
>> def join_as_strings(seq, sep):
>>     return sep.join([str(s) for s in seq])
>>
>> See? Everyone can opt to choose the Ruby way in Python too, it's just
>> not the default because it's deemed dangerous and a violation of
>> "explicit is better than implicit".
>
> And the Ruby community doesn't always follow that principle, so our
> default is the opposite.  Neither is inherently better.
>
>> I think this thread has been an interesting example of how similar the
>> two languages are - it started from "Python OO is a hack, Ruby is
>> better in FP also because it supports List Processing" (someone still
>> needs to tell me what List Processing is in Ruby) but it all really
>> boils down to are these small cultural differences. And they have been
>> hashed again and again in the past.
>
> I'm not the poster of that opinion, but I imagine he was referring to
> things like #each and #inject and the Enumerable module. I don't
> know Python, so I don't know what the analogues to these are, or
> if it has them at all.  Perhaps whenever he looked at Python, it 
> didn't.
>
> Ruby doesn't have list comprehensions like Python and Haskell do,
> though, if that's what you took it to mean.  Not having list
> comprehensions doesn't mean your bad at list processing, though.
> Otherwise Lisp would be bad at it (by default, at least), and Lisp
> stands for List Processing. :)
>
>> I bet you could use either language, and get exactly the same
>> productivity.
>
> I don't know that one is inherently better than the other at anything,
> really. It's mostly a matter of taste.  We should probably stop
> quibbling. :)
>
> Have a nice day.
>
> - Dan
>