Properties don't change when values are assigned? - ruby-on-rails-3

Question

I'm a bit of Ruby, noob, and there's some basic thing I'm not getting. I have something like this:
def my_method
attr1 = 'new 1 value'
attr2 = 'new 2 value'
puts "#{attr1} - #{attr2}"
puts "Should be same? #{to_s}"
end
def to_s
"#{attr1} - #{attr2}"
end
When I call my_method I get:
new 1 value - new 2 value
Should be same? old 1 value - old 2 value
Huh?

Answer 1

This is because in Ruby
x = y
is always an assignment of the value resulting from y to the variable x while
obj.x = y
is always sending the x= message to the object obj (with the value resulting from y).
In Ruby attributes/properties are really just methods! Thus, try:
self.attr1 = 'new 1 value'
self.attr2 = 'new 2 value'
On the other hand, y may or may not be a method call (read: property fetch). It depends on if there is already a variable y in scope or not because variables shadow methods. This is why attr1 and attr2 work in to_s without needing to be prefixed.
Happy coding.

Answer 2

There are two ways to do it. One is to use class-scoped variables instead of local variables:
class MyClass
def my_method
#attr1 = 'new 1 value'
#attr2 = 'new 2 value'
puts "#{#attr1} - #{#attr2}"
puts "Should be same? #{self.to_s}"
end
def to_s
"#{#attr1} - #{#attr2}"
end
end
m = MyClass.new
m.my_method
Output:
new 1 value - new 2 value
Should be same? new 1 value - new 2 value
The other way is to use attributes, which you have to specifically call as methods on self:
class MyClass
attr_accessor :attr1,:attr2
def my_method
self.attr1 = 'new 1 value'
self.attr2 = 'new 2 value'
puts "#{attr1} - #{attr2}"
puts "Should be same? #{self.to_s}"
end
def to_s
"#{attr1} - #{attr2}"
end
end
m = MyClass.new
m.my_method
This has the same output.

Answer 3

It's the scope attr1 and attr2 are local variables.
So when you're calling to_s it looking for attr_1 and attr_2 that you've declared (probably) in the class scope. Those won't get overwritten when you run my_method instead you just created a new variable in a smaller scope.
Try using #attr_1 and #attr_2 instead.
Check out Local Variable Gotchas