Calling private accessors

ruby-talk
1

Hi,

i bumbed into something weird today, and would like to know what's going
on... here's a contrived example:

class Test
  attr_reader :name

  def set_the_name(value)
    name = value
  end

  private

  def name=(value)
    @name = value
  end
end

test = Test.new
test.set_the_name "some name"
p test

the output of this on ruby 1.8.7 (as wel as on 1.9.2) is:

#<Test:0x7fef6dc8>

the name accessor wasn't called, but there was no error either

if i change the set_the_name method to this:

  def set_the_name(value)
    self.name = value
  end

then the output changes to this:

#<Test:0x7fef6da0 @name="some name">

there are two things i don't quite understand about this:
1) i thought private methods should never be called through self, and that
they are implicitely called on self. calling a non-accessor private method
on self does raise the expected error. why does the accessor need to be
called using self?
2) when calling the private accessor without using self, its implementation
clearly isn't executed but no exception is raised either... why is that?

2

Davy Brion wrote:

  def set_the_name(value)
    name = value
  end

To Ruby, that's an assignment to a local variable, which then drops out
of scope. That's why you have to do "self.name= value" to call the
method.

If it really were private, you'd need

  send(:name=, value)

although being private rather negates the purpose of an 'accessor' which
is to make values accessible :slight_smile:

when calling the private accessor without using self, its
implementation
clearly isn't executed but no exception is raised either... why is that?

Because it's perfectly legal to assign a value to a local variable :slight_smile:

···

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

3

Davy Brion wrote:
> def set_the_name(value)
> name = value
> end

To Ruby, that's an assignment to a local variable, which then drops out
of scope. That's why you have to do "self.name= value" to call the
method.

d'oh! of course :slight_smile:

If it really were private, you'd need

send(:name=, value)

although being private rather negates the purpose of an 'accessor' which
is to make values accessible :slight_smile:

in this case, i only want the accessor to be acessible to the class and its
subclasses, mainly because the subclasses need to be able to override the
'storage mechanism' (ie: backing field vs hash or something)... it's a bid
of an edge-case though :slight_smile:

> when calling the private accessor without using self, its
> implementation
> clearly isn't executed but no exception is raised either... why is that?

Because it's perfectly legal to assign a value to a local variable :slight_smile:

obviously :stuck_out_tongue:

···

On Fri, Sep 10, 2010 at 4:18 PM, Brian Candler <b.candler@pobox.com> wrote:

4

in this case, i only want the accessor to be acessible to the class and its
subclasses, mainly because the subclasses need to be able to override the
'storage mechanism' (ie: backing field vs hash or something)... it's a bid
of an edge-case though :slight_smile:

that is called 'protected' not 'private' - just that change should do
it.

-a