From: Gavin Sinclair <gsinclair@...>
Date: 2004-04-05T09:08:01+09:00
Subject: Re: deciding between ruby and python

On Monday, April 5, 2004, 8:44:59 AM, Dick wrote:

> * Gavin Sinclair <gsinclair@soyabean.com.au> [0447 18:47]:

>> On Monday, April 5, 2004, 12:09:58 AM, Yukihiro wrote:
>> > Maybe "join" should call "to_str" instead of "to_s" in the future.
 
>> Bad idea, IMO.  "join" is designed for returning a string.  It
>> therefore has the right to create strings as necessary for this
>> purpose.
>> "join" is similar to "puts" in this regard.

> Yeah, but it should be the objects decision whether it's able to provide a meaningful
> String version of itself.

I'm probably covering the same ground as DAB here, but there's a big
difference between a String *version* of itself and a String
*representation* of itself.  #to_str is aimed at the former, and #to_s
is aimed at the latter.

I believe that #join is interested in String *representations*, not
String *versions*, of objects.

And if you, as the high-level programmer, want a different
representation, there's always

  puts objects.map { |o| "... #{o.attribute} ..." }.join(", ")

In this light, think of

  puts objects.join(", ")

as using the **default string representation** of the objects.


> I generally use to_s for debugging, or any situation when I need
> to quickly 'see' the object - i.e. to_s provides a string
> representation of itself for *my* benefit.

I think you should be using #inspect here.  That's intended for
debugging, #to_s is not.  There's definitely a reason for having both
methods, and I think that's it.

> So 99% of my classes have a to_s method, but it's typically a
> list of its instance variables, for the very reason that puts calls it.

> join or anything else that wants a string to work with should
> ask the object to provide one, and to_str is there for that.

> If I haven't implemented that method I'm saying
> "I'm not a String, and I'm not going to pretend to be one".

That's not consistent with my understanding of the intentions of #to_s
and #to_str.  These methods (and #to_i/#to_int, etc.) have been a
reliable source of confusion for quite a while now.  I hope that they
get addressed in Pickaxe II or another educational resource.

Cheers,
Gavin