Method self.a= and a= create different instance variables

ruby-talk
1

i try this in irb .

irb(main):001:0> def a=(a)
irb(main):002:1> @a=a
irb(main):003:1> end
=> nil
irb(main):004:0> def a
irb(main):005:1> @a
irb(main):006:1> end
=> nil
irb(main):007:0> a=1
=> 1
irb(main):008:0> a
=> 1
irb(main):009:0> self.a=2
=> 2
irb(main):010:0> a
=> 1
irb(main):011:0> self.a
=> 2

a and a= should be private methods of Object. so call of a or self.a
should do the same thing. but it's not. i am now confused.

2

Hi --

···

On Wed, 26 Jul 2006, yuesefa wrote:

i try this in irb .

irb(main):001:0> def a=(a)
irb(main):002:1> @a=a
irb(main):003:1> end
=> nil
irb(main):004:0> def a
irb(main):005:1> @a
irb(main):006:1> end
=> nil
irb(main):007:0> a=1
=> 1
irb(main):008:0> a
=> 1
irb(main):009:0> self.a=2
=> 2
irb(main):010:0> a
=> 1
irb(main):011:0> self.a
=> 2

a and a= should be private methods of Object. so call of a or self.a
should do the same thing. but it's not. i am now confused.

When you write:

   a = 1

Ruby parses that as a local variable assignment. In other words,
methods ending in = always require that you provide an explicit
receiver (in this case "self").

David

--
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dblack@wobblini.net => me

3

yuesefa <yuesefa@gmail.com> writes:

i try this in irb .

irb(main):001:0> def a=(a)
irb(main):002:1> @a=a
irb(main):003:1> end
=> nil
irb(main):004:0> def a
irb(main):005:1> @a
irb(main):006:1> end
=> nil
irb(main):007:0> a=1
=> 1
irb(main):008:0> a
=> 1

irb(main):010:0> @a
=> nil
irb(main):011:0> self.a
=> nil
That means that not the method a= was called, but the local variable a was set
to one.

irb(main):009:0> self.a=2
=> 2

Here you expicitly call the method, so @a is set to 2.

irb(main):010:0> a
=> 1

But the local variable a is still 1.

irb(main):011:0> self.a
=> 2

Here the method a is explicitly called, so you get what you expected.

a and a= should be private methods of Object. so call of a or self.a
should do the same thing. but it's not. i am now confused.

It's simply because the ruby-interpreter can't tell what you want when you
write a=1 -- do you want to set a to 1, or do you want to call the method a?

HTH,
Tom

4

thank both of u, i am clear now :slight_smile:

5

also,

@a

will give you the same as

self.a

which makes sense because you are "inside" the definition of Object:

irb(main):085:0> self
=> #<Object:0x277fa2c @a=7>

Les

···

On 7/25/06, dblack@wobblini.net <dblack@wobblini.net> wrote:

Hi --

On Wed, 26 Jul 2006, yuesefa wrote:

> i try this in irb .
>
> irb(main):001:0> def a=(a)
> irb(main):002:1> @a=a
> irb(main):003:1> end
> => nil
> irb(main):004:0> def a
> irb(main):005:1> @a
> irb(main):006:1> end
> => nil
> irb(main):007:0> a=1
> => 1
> irb(main):008:0> a
> => 1
> irb(main):009:0> self.a=2
> => 2
> irb(main):010:0> a
> => 1
> irb(main):011:0> self.a
> => 2
>
> a and a= should be private methods of Object. so call of a or self.a
> should do the same thing. but it's not. i am now confused.

When you write:

   a = 1

Ruby parses that as a local variable assignment. In other words,
methods ending in = always require that you provide an explicit
receiver (in this case "self").