Calling a reader from a writer

ruby-talk
1

class Test
  def x
    @x + '_instance'
  end

  def x=(v)
    @x = v
    self.x # also tried `x'
  end
end

t = Test.new
puts t.x=('test_x')
  => test_x
puts t.x
  => test_x_instance

Why doesn't the first puts output 'test_x_instance'? I would think that
the self.x call in the writer would call the reader.

How can one call the reader from the writer method?

-pachl

2

Hi,

At Sat, 14 Oct 2006 10:25:11 +0900,
clintpachl wrote in [ruby-talk:219643]:

t = Test.new
puts t.x=('test_x')
  => test_x
puts t.x
  => test_x_instance

An assignment expression always returns the assigned value,
regardless of the implementation of the setter method.

···

--
Nobu Nakada

3

Hi --

class Test
def x
   @x + '_instance'
end

def x=(v)
   @x = v
   self.x # also tried `x'
end
end

t = Test.new
puts t.x=('test_x')
=> test_x
puts t.x
=> test_x_instance

Why doesn't the first puts output 'test_x_instance'? I would think that
the self.x call in the writer would call the reader.

This just came up today on IRC. I'd forgotten about it, but was
reminded.

The writer method allows you to use the assignment-like syntax:

   t.x = value

Since the goal of this is to make the method call look and feel more
assignment-like, and assignments return their right-hand side, the
writer-method calls also return their right-hand side, rather than the
last value in the method.

How can one call the reader from the writer method?

You are calling the reader, but the magic rhs value overrides it. I
haven't found any way to circumvent it.

David

···

On Sat, 14 Oct 2006, clintpachl wrote:

--
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails" [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog) [2] | Co-director, Ruby Central, Inc. [4]
[1] Ruby for Rails | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com | [4] http://www.rubycentral.org

4

David, you are right on. Now that I think about it, Ruby does the
natural thing. I was just experimenting and thought it was weird that
my return value was not returning. I guess I needed to step outside the
box.

-pachl

···

On Oct 13, 8:02 pm, dbl...@wobblini.net wrote:

On Sat, 14 Oct 2006, clintpachl wrote:
> class Test
> def x
> @x + '_instance'
> end

> def x=(v)
> @x = v
> self.x # also tried `x'
> end
> end

> t = Test.new
> puts t.x=('test_x')
> => test_x
> puts t.x
> => test_x_instance

> Why doesn't the first puts output 'test_x_instance'? I would think that
> the self.x call in the writer would call the reader.This just came up today on IRC. I'd forgotten about it, but was
reminded.

The writer method allows you to use the assignment-like syntax:

   t.x = value

Since the goal of this is to make the method call look and feel more
assignment-like, and assignments return their right-hand side, the
writer-method calls also return their right-hand side, rather than the
last value in the method.

> How can one call the reader from the writer method?

You are calling the reader, but the magic rhs value overrides it. I
haven't found any way to circumvent it.