Here's the code:
class Something attr_accessor :x def initialize(x) @x = x end def get_x x end end something = Something.new(5) something.get_x # => 5 Why interpreter returns 5 if x is just a local variable in get_x method? Thanks
Add a comment |
3 Answers
x is also a method. attr_accessor :x adds x= and x to your class. So, get_x is calling the x method, and returning the value for @x. see http://www.rubyist.net/~slagell/ruby/accessors.html for details.
Comments
attr_accessor :x adds two methods for you:
def x=(val) @x = val end def x @x end So you don't actually need get_x getter if you've added attr_accessor method.
UPD
So the question is
class Something attr_accessor :x def initialize(x) @x = x end def set_x=(new) x = new end end Why won't x = new call default x setter: because default x setter is an instance method so you can call it for an object (Something instance) but not in your class like you try.
10 Comments
megas
But what if we have another method def set_x(new_x) x = new_x end, why interpreter doesn't assume that is x=(val) method?
fl00r
you can write as many setters as you want.
attr_accessor is just a "helper" it creates two methods for you, but you are free to create as much as you needmegas
The question is not how to make better, it's compiler trick issue.
muffinista
Oh wait now I see what you're saying. If you use 'self.x = new_x' it actually does do that. This just seems like trying to break the interpreter. You should always be explicit about what variable/method you want in internal code.
Phrogz
The other interesting edge case can be seen as the interpreter guesses if you're accessing a local variable or invoking a method on yourself. Try this:
def x; "method"; end; p x; x = 42; p x. The first x invokes the method (because no local variable with that name exists), but the second identical x reads the local variable. Local variables mask methods in the same scope unless you prefix with self. |
The attr_accessor defines a method x (and the setter x=) which gets called in get_x.
>> something.methods.grep /^x/ => [:x, :x=] 