From: Dan Zwell <dzwell@...>
Date: 2007-08-01T04:15:03+09:00
Subject: Re: Unexpected behavior with multidimensional arrays

Tim Pease wrote:
> On 7/31/07, Armin Armbruster <aarmbruster@ndigital.com> wrote:
>> Frankly, just as the poster in ruby-talk I have my troubles accepting
>> this not being a violation of the principle of least surprise (and yes,
>> I come from a C programming background).
>> Anyhow, now I know it and (hopefully) will remember it the next time. I
>> still have not glue why one would want an array whose elements are
>> referencing the same object. Does anybody know an example where this is
>> actually useful?
>>
> 
> In ruby, constructing an array and adding the same object multiple
> times is the least surprising behavior. Creating several copies of the
> object would be "hidden behavior" inside the array initializer, and
> hidden behavior is usually a bad thing.
> 

I agree with you on this point. However, I can't think of a situation 
where the second argument is useful. For example,
   ary = Array.new(n, 0)
can be replaced with
   ary = Array.new(n) {0}

So I ask, is this functionality (creating an array with 2 arguments) 
useful to people? Because I think everybody makes this mistake once, and 
that certainly seems to qualify as being counter-intuitive.

In fact, anything that in done with Array.new(n, obj) can be done with 
Array.new(n) {obj}. Am I mistaken? See the following:
 >> inner = []
=> []
 >> ary = Array.new(3) {inner}
=> [[], [], []]
 >> inner << "hi"
=> ["hi"]
 >> ary
=> [["hi"], ["hi"], ["hi"]]

The above does the same thing as ary = Array.new(3, []), but needs one 
more line of code.

What does everyone think?

Dan