Method vs variable assigment

ruby-talk
1

I can't understand why this script

#!/usr/bin/ruby
class A
  attr_accessor :v

  def test
    p @v
  end

  def mod_explicit_setter
    self.v = "explicit setter"
  end

  def mod_setter
    v = "setter"
  end

  def mod_direct
    @v = "direct"
  end
end

a = A.new
p a.methods - Object.new.methods

a.mod_setter; a.test
a.mod_direct; a.test
a.mod_setter; a.test
a.mod_explicit_setter; a.test

have this output

["mod_setter", "mod_direct", "v", "v=", "mod_explicit_setter", "test"]
./vm.rb:7: warning: instance variable @v not initialized
nil <- correct, v is a local variable
"direct" <- correct
"direct" <- correct? v= is an already seen method
"explicit setter" <- correct

I thought that, once ruby sees a methods, it prefers to call that method
instead of creating a new local variable.

···

--
Gioele <dev@gioelebarabucci.com>

2

Hi --

···

On Sun, 23 Apr 2006, Gioele Barabucci wrote:

I can't understand why this script

> #!/usr/bin/ruby
> class A
> attr_accessor :v
>
> def test
> p @v
> end
>
> def mod_explicit_setter
> self.v = "explicit setter"
> end
>
> def mod_setter
> v = "setter"
> end
>
> def mod_direct
> @v = "direct"
> end
> end
>
> a = A.new
> p a.methods - Object.new.methods
>
> a.mod_setter; a.test
> a.mod_direct; a.test
> a.mod_setter; a.test
> a.mod_explicit_setter; a.test

have this output

> ["mod_setter", "mod_direct", "v", "v=", "mod_explicit_setter", "test"]
> ./vm.rb:7: warning: instance variable @v not initialized
> nil <- correct, v is a local variable
> "direct" <- correct
> "direct" <- correct? v= is an already seen method
> "explicit setter" <- correct

I thought that, once ruby sees a methods, it prefers to call that method
instead of creating a new local variable.

No; actually whenever it sees this:

   var = value

it assumes that var is a local variable. So for methods ending in =
you get the syntactic sugar on the right (= instead of .=()) but not
on the left (you have to indicate the receiver explicitly).

David

--
David A. Black (dblack@wobblini.net)
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)

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