From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-12-06T06:24:29+09:00
Subject: Re: different output for same expression?

On Sat, Dec 5, 2009 at 6:43 PM, Paul Smith <paul@pollyandpaul.co.uk> wrote:
> On Sat, Dec 5, 2009 at 5:14 PM, Steven Arnold
> <stevena@arnold-software.com> wrote:
>> Forgive me if this is an elementary question and I am missing something obvious, but there is a behavior in Ruby that puzzles me a lot.
>>
>> I don't see why the two blocks below do not produce the same output.  One displays the numerically sorted array and the other does not.
>>
>> # Block 1
>> myarray = ["210", "22"]
>> myarray = myarray.sort do |a,b|
>>    a.to_i <=> b.to_i
>> end
>> puts myarray
>>
>> # Block 2
>> myarray = ["210", "22"]
>> puts myarray.sort do |a,b|
>>    a.to_i <=> b.to_i
>> end
>>
>> In one case, I reassign myarray to the return value of the sort method for myarray and then print myarray.  In the other case, I just directly print the return value of the sort method.  Shouldn't the return value be the same in both cases, and therefore the output also the same?
>
> Precedence.
>
> Note that "puts myarray" returns myarray.

This is not correct. puts returns nil:

irb(main):004:0> myarray = ["210", "22"]
=> ["210", "22"]
irb(main):005:0> puts myarray
210
22
=> nil


> There's an ambiguity in
> your code that's being resolved dur to precedence.  Look at the
> following:
>
> (puts myarray).sort do ...
>
> puts (myarray.sort do ... )
>
> You're expecting the second, but you're getting the first.

This is not correct. What you are getting is:

puts (myarray.sort) do ...

and you are outputting the array in alphanumerical order of its string contents.
The block is passed to the puts method, and silently ignored.

> However, puts myarray.sort { ... will work the way you want, because {
> has higher precedence than do.

This works too if you want to keep the do...end:

irb(main):010:0> puts(myarray.sort do |a,b|
irb(main):011:2* a.to_i <=> b.to_i
irb(main):012:2> end)
22
210
=> nil

Jesus.