Confusion with singleton method call

ruby-talk
1

C:\>irb --simple-prompt
DL is deprecated, please use Fiddle

class Foo
def talk
p "huanng"
end
end

=> nil

module Bar
def talk
p "hunnggg"
end
end

=> nil

foo = Foo.new

=> #<Foo:0x20493c0>

class << foo
def talk
super
return
p "hukkangg"
end
include Bar
end

=> #<Class:#<Foo:0x20493c0>>

part - A

foo.talk

"hunnggg"
=> nil

Part - B

foo.class.instance_method(:talk).bind(foo).call

"huanng"
=> "huanng"

Can anyone help me to understand the difference between the two call to
`talk`? or How part B bypass the call to singleton method `talk` to
class Foo s `talk` ?

···

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2

foo.class.instance_method(:talk) is specifically the method that
returns "huanng" (you need to pick less ambiguous choices of output)

class Foo
  def talk
    p "talk"
  end
end

Foo.instance_method(:talk)

=> #<UnboundMethod: Foo#talk>

If you bind it to an object, it is no longer unbound:

Foo.instance_method(:talk).bind(Foo.new)

=> #<Method: Foo#talk>

You're calling this Method instance, using the state in your instance
of Foo. This is different from sending message to an instance of Foo
(with foo.talk) and letting it do a method look-up. In the latter
case, it sees the singleton method as part of the look-up.

3

What I know singleton methods can be called by the objects, on which it
is defined. Now in the below example `C` is also
an object of `Class` and singleton method `a_class_method` defined on
the `Class` object `C`. So how does another `Class` object `D` able
to call `a_class_method`? How does object `individuation` principle
holds in this example?

class C
end
#=> nil
def C.a_class_method
puts "Singleton method defined on #{self}"
end
#=> nil
C.a_class_method
Singleton method defined on C
#=> nil
class D < C
end
#=> nil
D.a_class_method
Singleton method defined on D
#=> nil

···

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4

Why the `singleton` methods can't be defined on
`Fixnum`,`Bignum`,`Float`,`Symbol` class objects, but ` FalseClass` and
`TrueClass` can have?

    C:\>ruby -v
    ruby 2.0.0p0 (2013-02-24) [i386-mingw32]

    C:\>irb --simple-prompt
    DL is deprecated, please use Fiddle
    11111111111.class
    #=> Bignum
    # class << 11111111111 ; end
    #TypeError: can't define singleton
    # from (irb):2
    # from C:/Ruby200/bin/irb:12:in `<main>'

    1111.class
    #=> Fixnum
    class << 1111 ; end
    #TypeError: can't define singleton
    # from (irb):4
    # from C:/Ruby200/bin/irb:12:in `<main>'

    11.11.class
    #=> Float
    class << 11.11 ; end
    #TypeError: can't define singleton
    # from (irb):6
    # from C:/Ruby200/bin/irb:12:in `<main>'

    :name.class
    #=> Symbol
    class << :name ; end
    #TypeError: can't define singleton
    # from (irb):8
    # from C:/Ruby200/bin/irb:12:in `<main>'

`true` and `false` object also has fixed `object_id`. Why are then they
allowed to have `singleton` methods on them?

    C:\>irb --simple-prompt
    DL is deprecated, please use Fiddle

    def true.test ; end
    #=> nil

    class << true
    def show
    p "How possible?"
    end
    end
    #=> nil

    true.show
    #"How possible?"
    #=> "How possible?"

    true.object_id
    #=> 2
    true.object_id
    #=> 2

    class << false
    def show
    p "How possible?"
    end
    end
    #=> nil

    false.show
    #"How possible?"
    #=> "How possible?"

    false.object_id
    #=> 0
    false.object_id
    #=> 0

···

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5

Can anyone help me here?

···

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6

true.singleton_class #=> TrueClass
false.singleton_class #=> FalseClass
nil.singleton_class #=> NilClass

thats why each try to define singleton classes on this objects are
turned into normal method defining on the real classes

···

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7

Love U Ruby wrote in post #1101669:

What I know singleton methods can be called by the objects, on which it
is defined. Now in the below example `C` is also
an object of `Class` and singleton method `a_class_method` defined on
the `Class` object `C`. So how does another `Class` object `D` able
to call `a_class_method`? How does object `individuation` principle
holds in this example?

class C
end
#=> nil
def C.a_class_method
puts "Singleton method defined on #{self}"
end
#=> nil
C.a_class_method
#Singleton method defined on C
#=> nil
class D < C
end
#=> nil
D.a_class_method
#Singleton method defined on D
#=> nil

If you did D.method :a_class_method you'll see:
#<Method: D(C).a_class_method>

This happens because D's singleton class inherits from C's singleton
class, which happens because D inherits from C (and as such, D _is_ C).

···

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8

Think about it. You're trying to define directly on a NUMBER, even though its class is BigNum, numbers can't have singletons assigned to them. Now if you did class << BigNum that'd be different.

Same thing for when you attempt to assign to a symbol. Now if you did class << Symbol that'd be different.

Dude, if you're going to try complex stuff like this, use your friggin head. You keep attempting to do dumb ass stuff, but don't have a clue to what you're doing. You're not thinking, nor even attempting to reason it out. It didn't dawn on you that NUMBERS are different than their base class? What good would defining a singleton on the number 11 do? NOTHING!

···

Love U Ruby <mailto:lists@ruby-forum.com>
March 17, 2013 11:39 PM
Can anyone help me here?

Love U Ruby <mailto:lists@ruby-forum.com>
March 14, 2013 1:38 PM
C:\>irb --simple-prompt
DL is deprecated, please use Fiddle

class Foo
def talk
p "huanng"
end

=> nil

module Bar
def talk
p "hunnggg"
end

=> nil

foo = Foo.new

=> #<Foo:0x20493c0>

class<< foo
def talk
super
return
p "hukkangg"
end
include Bar
end

=> #<Class:#<Foo:0x20493c0>>

part - A

foo.talk

"hunnggg"
=> nil

Part - B

foo.class.instance_method(:talk).bind(foo).call

"huanng"
=> "huanng"

Can anyone help me to understand the difference between the two call to
`talk`? or How part B bypass the call to singleton method `talk` to
class Foo s `talk` ?

--
D. Deryl Downey

  "The bug which you would fright me with I seek" - William Shakespeare - The Winter's Tale, Act III, Scene II - A court of Justice.

9

Hans Mackowiak wrote in post #1102040:

true.singleton_class #=> TrueClass
false.singleton_class #=> FalseClass
nil.singleton_class #=> NilClass

thats why each try to define singleton classes on this objects are
turned into normal method defining on the real classes

Thanks Hans. It sounds good. I tried the same in my IRB. But didn't
think that way.

The most valuable thing that I learned from here is the "Thinking
Approach", which is helping a lot.

@John thank you also. As I got some more valuables thing to read from
the search "can't define singleton ruby". :slight_smile:

Thanks as usual.

···

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10

D. Deryl Downey wrote in post #1102022:

Dude, if you're going to try complex stuff like this, use your friggin
head. You keep attempting to do dumb ass stuff, but don't have a clue to
what you're doing. You're not thinking, nor even attempting to reason it
out. It didn't dawn on you that NUMBERS are different than their base
class? What good would defining a singleton on the number 11 do?
NOTHING!

I don't know how much you understand my above question,which is so
valid.

From the doc: http://www.ruby-doc.org/core-2.0/Fixnum.html

Clearly mentioned that - ***There is effectively only one Fixnum object
instance for any given integer value, so, for example, you cannot add a
singleton method to a Fixnum.**

The same I agreed for Bignum,FLoat and Symbol.

Now the `true`,`false` and `nil` also has fixed Object_id, But why they
are allowed to have singleton class on them. -- This is my curiosity to
know and I think which is to legitimate.

Thanks.

···

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11

That nasty thing google again - it always amazes me why they put
descriptions of errors sometimes.

"can't define singleton ruby"

You're welcome as usual

John

···

On Sun, Mar 17, 2013 at 10:43 PM, Love U Ruby <lists@ruby-forum.com> wrote:

D. Deryl Downey wrote in post #1102022:

>
> Dude, if you're going to try complex stuff like this, use your friggin
> head. You keep attempting to do dumb ass stuff, but don't have a clue to
> what you're doing. You're not thinking, nor even attempting to reason it
> out. It didn't dawn on you that NUMBERS are different than their base
> class? What good would defining a singleton on the number 11 do?
> NOTHING!

I don't know how much you understand my above question,which is so
valid.

From the doc: Class: Fixnum (Ruby 2.0.0)

Clearly mentioned that - ***There is effectively only one Fixnum object
instance for any given integer value, so, for example, you cannot add a
singleton method to a Fixnum.**

The same I agreed for Bignum,FLoat and Symbol.

Now the `true`,`false` and `nil` also has fixed Object_id, But why they
are allowed to have singleton class on them. -- This is my curiosity to
know and I think which is to legitimate.

Thanks.

--
Posted via http://www.ruby-forum.com/\.