Confusion about singleton method definition

Ruby
1

Hi fellow Rubists,

I’m just learning Ruby from The Well-grounded Rubist book and I cann’t
understand why I cann’t get the same results as in author’s example.

It’s about the difference between defining singleton method directly on
an object and using class << construct.
Rephrased example follows:

MYCONST=666

myobj = Object.new

class << myobj
MYCONST=333
end

def myobj.outer_const
puts MYCONST
end

class << myobj
def inner_const
puts MYCONST
end
end

myobj.inner_const call displays 333 (singleton constant value) as
expected,
however myobj.outer_const call also displays 333 whereas it should
display the value of outer (global) MYCONST definition, ie. 666.

Did changed language definition recently somehow or is the example
and/or description in the book simply flawed ?

2

myobj.outer_const and instance methods defined in the anonymous class
have the same context, which is expected to be differerent from that of
the top level. MYCONST in both places binds to the same `self’ (myobj).

puts self

myobj = Object.new

class << myobj
def foo
puts self
end
end

def myobj.bar
puts self
end

myobj.foo
myobj.bar

Outputs:
main
#Object:0xae5358
#Object:0xae5358

Tried with both 1.9.2 and 1.8.7 =)

3

Su Zhang> Thanks, but that confirms my results. The books preface states
it covers Ruby ver. 1.9.1 and I would wonder if it’s valid no more for
Ruby 1.9.2 ?

4

Anybody else can confirm there is no difference between constants scope
resolution at various kinds of singleton methods definiton?

5

On Mon, Nov 29, 2010 at 5:30 PM, David U. [email protected]
wrote:

puts MYCONST
end
end

myobj.inner_const call displays 333 (singleton constant value) as
expected,
however myobj.outer_const call also displays 333 whereas it should
display the value of outer (global) MYCONST definition, ie. 666.

Does it?

16:55:39 ~$ allruby r.rb
CYGWIN_NT-5.1 padrklemme2 1.7.7(0.230/5/3) 2010-08-31 09:58 i686 Cygwin

ruby 1.8.7 (2008-08-11 patchlevel 72) [i386-cygwin]
333
666

ruby 1.9.1p430 (2010-08-16 revision 28998) [i386-cygwin]
333
666

jruby 1.4.0 (ruby 1.8.7 patchlevel 174) (2009-11-02 69fbfa3) (Java
HotSpot™ Client VM 1.6.0_21) [x86-java]
333
666
16:55:55 ~$ cat r.rb

MYCONST=666

myobj = Object.new

class << myobj
MYCONST=333
end

def myobj.outer_const
puts MYCONST
end

class << myobj
def inner_const
puts MYCONST
end
end

myobj.inner_const
myobj.outer_const
16:56:57 ~$

Did changed language definition recently somehow or is the example
and/or description in the book simply flawed ?

Can you show exactly the code you executed?

Kind regards

robert

6

On Tue, Nov 30, 2010 at 9:58 AM, Robert K.
[email protected]wrote:

myobj = Object.new
def inner_const
Does it?
666

puts MYCONST
Can you show exactly the code you executed?

Kind regards

robert

–
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

I get that result for 1.9.2

$ rvm r.rb
1.8.7(jruby-1.5.2)
333
666
1.8.7(jruby-1.5.3)
333
666
1.9.2(macruby-0.7)
333
666
1.8.7(rbx-1.1.0-20100923)
333
666
1.8.6(ruby-1.8.6-p399)
333
666
1.8.7(ruby-1.8.7-p249)
333
666
1.8.7(ruby-1.8.7-p302)
333
666
1.9.1(ruby-1.9.1-p378)
333
666
1.9.2(ruby-1.9.2-p0)
333
333

$ cat r.rb
MYCONST=666

myobj = Object.new

class << myobj
MYCONST=333
end

def myobj.outer_const
puts MYCONST
end

class << myobj
def inner_const
puts MYCONST
end
end

puts “#{RUBY_VERSION}(#{ENV[‘RUBY_VERSION’]})”
myobj.inner_const
myobj.outer_const

7

On Tue, Nov 30, 2010 at 8:35 PM, David U. [email protected]
wrote:

Anybody else can confirm there is no difference between constants scope
resolution at various kinds of singleton methods definiton?

in ruby 1.9.2, your example will provide no difference.
if you want to access the outside constant (in ruby 1.9.2), use
::MYCONST

best regards -botp