Ruby - Instance variables
| | Ruby user's guide | Instance variables | |
An instance variable has a name beginning with @, and its
scope is confined to whatever object self refers to.
Two different objects, even if they belong to the same class, are
allowed to have different values for their instance variables.
From outside the object, instance variables cannot be altered or even
observed (i.e., ruby's instance variables are never public)
except by whatever methods are explicitly provided by the
programmer. As with globals, instance variables have the
nil value until they are initialized.
Instance variables of ruby do not need declaration. This
implies a flexible structure of objects. In fact, each instance
variable is dynamically appended to an object when it is first
referenced.
ruby> class InstTest
| def set_foo(n)
| @foo = n
| end
| def set_bar(n)
| @bar = n
| end
| end
nil
ruby> i = InstTest.new
#<InstTest:0x83678>
ruby> i.set_foo(2)
2
ruby> i
#<InstTest:0x83678 @foo=2>
ruby> i.set_bar(4)
4
ruby> i
#<InstTest:0x83678 @foo=2, @bar=4> |
Notice above that i does not report a value for
@bar until after the set_bar method is
invoked.
