From: RichardOnRails <RichardDummyMailbox58407@...>
Date: 2009-10-30T10:20:06+09:00
Subject: Ruby doesn't implement x++ for Fixnum's because ???

Hi,

In The Well Grounded Rubyist (which,  along with The Ruby Way, I
love),  Dave Black presents a justification for the x++ omission in
Ruby.  I thought I'd see whether I could implement just the
incrementing portion of C's x++ functionality (without the prefix/
postfix issues) in pure Ruby.  I wasn’t willing to delve into Matz’
implementation of higher-level Ruby functions or low-level C/C++
code.  Below is what I came up with.

Q1.  Test 1 failed, I imagine,  because the interpret thought “Ah, 7’s
a Fixnum which I ‘ve seen billions of times, so I know what to do with
it.”  Thus,  it ignored my over-riding definition of Fixnum.  So I
call it “compiler error”, to use the vernacular,  by reporting that x
had no method “pp”.  Am I all wet?

Test 2 passed,  but it with a couple of anomalies:

Q2. x.to_s yielded x’s class and address, suggesting x had become a
“semi-Fixed Num”, i.e, x now stored a REFERENCE to the to x’s data,
rather than the immediate storage of the data, as interpreter is wont
to do with Fixnum’s.  Am I all wet?

Q3. y.inspect yielded only it’s value (8) and nothing else,
suggesting the x.pp yielded a full-fledged Fixnum.    Am I all wet?

Dave Black argues that since Fixnum values use immediate storage
rather than referenced storage, x=1;x++ would be akin to changing 1
into 2.  This example somewhat supports that view,  but the
interpreter sidestepped the matter by creating a reference for x’s
value and an immediate value for y (=x.pp).

Any ideas,
Richard


class FixNum
  attr :val
  def initialize (fixnum)
    puts "Initializing object %d" % fixnum
    raise "Initializer not a Fixnum" if
	fixnum.class != Fixnum
    puts "\nInitializing Fixnum to %d" % fixnum
    @val = fixnum
  end

  def pp
    @val+=1
  end
end

# Test 1 (Failure)
x = 7;  y = x.pp; z =x.class # undefined method `pp' for 7:Fixnum
(NoMethodError)

# Test 2 (Success)
x = FixNum.new(7);  y = x.pp; z =x.class
puts [x.to_s, y.inspect, z.to_s].join("; ") # => <FixNum:0x2b62694>;
8; FixNum