From: Brian Candler <b.candler@...>
Date: 2009-04-30T19:30:33+09:00
Subject: Re: Random Access using IO#pos in code blocks

Robert Klemme wrote:
> I do have to admit though that I
> do not know when the object is allocated (i.e. at time of match or
> when referencing $`).

Experiment suggests the MatchData is created immediately on the match, 
and the string is instantiated lazily from that. This makes sense; it 
would be very inefficient to allocate strings for $`, $1, $2, $3, ... $' 
when maybe none of them will be used. But the MatchData object has the 
original string plus all the offsets.

def count(klass)
  c = 0
  ObjectSpace.each_object(klass) { c += 1 }
  c
end

str = "  foo bar baz  "

c1 = [count(MatchData), count(String)]

str =~ /(\w+)/

c2 = [count(MatchData), count(String)]

x = $~

c3 = [count(MatchData), count(String)]

y = $`

c4 = [count(MatchData), count(String)]

puts [c1,c2,c3,c4].inspect
# [[0, 188], [1, 188], [1, 188], [1, 189]]
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