From: Joel VanderWerf <vjoel@...>
Date: 2005-10-23T10:27:01+09:00
Subject: Re: what's the difference?

Daniel Sch�le wrote:
> Hello @*,
> 
> irb(main):105:0> 10.times { d={}; puts d.object_id }
> 537970544
> 537969634
> 537969504
> 537969404
> 537969354
> 537969334
> 537969304
> 537969274
> 537969244
> 537969184
> => 10
> irb(main):106:0>
> 
> 10 different Hash objects are constructed and their id's are printed out
> why doesn't the following do the same?
> 
> irb(main):106:0> 10.times { puts {}.object_id }
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> => 10
> irb(main):107:0>

Ruby's parser associates the second line like this:

irb(main):001:0> 10.times { (puts {}).object_id }

Which does a "puts {}" ten times, and prints 10 blank lines. the
#object_id method is called on the return value of puts (which is nil)
and is never printed.

But:

irb(main):002:0> 10.times { puts({}.object_id) }
-606176002
-606176022
-606176042
-606176072
-606176092
-606176112
-606176132
-606176162
-606176182
-606176202
=> 10

Why does this funny association happen? Ruby thinks the {} without
parens is a block, not a hash:

irb(main):004:0> puts {}

=> nil
irb(main):005:0> puts do end

=> nil
irb(main):006:0> puts {exit}

=> nil

The block is silently ignored by ruby.

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407