Directly accessing an instance variable vs. Using an accessor method

self.attribute calls the method attribute.
self.attribute = value calls the method attribute= with the argument value.
@attribute and @attribute = value get/set the value of the instance variable @attribute.

So basically they’re two entirely different things.

However if you call attr_accessor :attribute it defines the method attribute to return @attribute and the method attribute=(value) to set @attribute = value. So in that case, there is no difference.