How to remove a method from an object?

Ruby
1

hello everyone,

how can I remove a method from an object, without impacting future
instances of its class ?

say:

class Server
def print
puts ‘hello’
end
end

s1 = Server.new
s1.print #this work

#now remove print from s1 somehow…

s1.print #this should hit method_missing

s2 = Server.new
s2.print # this should work fine as well…

Thanks for any help

2

class Server
attr_accessor :shh

def initialize(f=false)
@shh = f
end

def print
if @shh
self.send(:method_missing)
else
puts ‘hi there’
end
end

def method_missing
puts ‘I look forward to seeing better ways of doing this!’
end

end

s = Server.new
s.print

s2 = Server.new(true)
s2.print

s.print

On Jan 10, 12:32 am, Valerio S. [email protected]

3

On Jan 10, 2008 4:35 PM, Valerio S. [email protected]
wrote:

how can I remove a method from an object, without impacting future
instances of its class ?

the method is defined in the class, if you remove it, others will be
affected.

try using singleton_method instead…(and yes, you can remove
singleton methods w your hearts content; but since these methods
belong to a particular object, you might not even bother removing…
:slight_smile:

kind regards -botp

4

Alle giovedì 10 gennaio 2008, Valerio S. ha scritto:

end
s2.print # this should work fine as well…

Thanks for any help

This should work:

class Server
def print
puts “hello from #{object_id}”
end
end

s1 = Server.new
s1.print

class << s1
undef_method :print
end

s2 = Server.new
s2.print
begin s1.print
rescue NoMethodError
puts “undefined method ‘print’ for #{s1.object_id}”
end

=>
hello from -605995538
hello from -605995648
undefined method ‘print’ for -605995538

As you can see from the ids displayed by the print method, after
removing the
method from the singleton class of s1, only the call to s2.print works;
the
call to s1.print raises a NoMethodError exception.

I hope this helps

Stefano

5

Alle giovedì 10 gennaio 2008, botp ha scritto:

end

i mean will undef_ do a remove or what?

but anyway, that is cool Stefano. thanks for the new i’ve just learned.

kind regards -botp

Well, in general remove_method will remove it only from the class where
it’s
called. If a superclass defines the same method, the superclass’s method
will
be called. According to ri, instead, undef_method, prevents the class
from
responding to the method at all. Here’s an example showing the
difference

class A
def test
puts “test for class A”
end
end

class B < A
def test
puts “test for class B”
end
end

b = B.new
b.test
=> test for class B

class B
remove_method :test
end

b.test
=> test for class A

class B
undef_method :test
end

b.test
=> undefined method `test’ for #<B:0xb7c9a754> (NoMethodError)

In my previous post, used undef_method instead of remove_method thinking
(without trying it) that remove_method would only remove it from the
singleton class. I tried it now, and I saw it works with both methods.
It
seems singleton classes are treated in a different way.

Stefano

6

On Jan 10, 2008 11:54 AM, Stefano C. [email protected]
wrote:

class << s1
called. If a superclass defines the same method, the superclass’s method will
def test
end

In my previous post, used undef_method instead of remove_method thinking
(without trying it) that remove_method would only remove it from the
singleton class. I tried it now, and I saw it works with both methods.
Does it? I cannot reproduce that behavior:

class << Class::new {
def a; 42 end
}
remove_method :a
end

singleton.rb:7:in remove_method': method a’ not defined in Class
(NameError)
from singleton.rb:7

It
seems singleton classes are treated in a different way.
IIRC Mauricio F. has shown that undef_method leaked (or still
leaks) so normally I would use remove_method
whenever possible, which is however not the case here.
Cheers
Robert

–
http://ruby-smalltalk.blogspot.com/

Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein

7

On Jan 10, 2008 6:12 PM, Stefano C. [email protected] wrote:

class << s1
undef_method :print
end

ah, undef_,

how does it compare then if i do,
class << s1
remove_method :print
end

i mean will undef_ do a remove or what?

but anyway, that is cool Stefano. thanks for the new i’ve just learned.

kind regards -botp

8

Alle giovedì 10 gennaio 2008, Robert D. ha scritto:

Does it? I cannot reproduce that behavior:

class << Class::new {
def a; 42 end
}
remove_method :a
end

singleton.rb:7:in remove_method': methoda’ not defined in Class
(NameError) from singleton.rb:7

You’re right, it doesn’t work. I didn’t look close enough at the output.

Stefano

9

Brian.LeRoux ha scritto:

else

s = Server.new
On Jan 10, 12:32�am, Valerio S. [email protected]

� � � �puts ‘hello’
s2 = Server.new
s2.print # this should work fine as well…

Thanks for any help

Maybe it is not what the original post asked for, but I could not
resist…

class Server
def initialize(add_print_method=false)
if (add_print_method)
def self.print
puts “Hi #{self.object_id.to_s(16)}”;
end
end

puts "Object #{self.object_id.to_s(16)} created"

end
end

a=Server.new(true)
b=Server.new

a.print # prints “Hi …”
b.print # raises NoMethodError