Ruby - Variables
| | Ruby user's guide | Variables | |
Ruby has three kinds of variables, one kind of constant and
exactly two pseudo-variables. The variables and the constants
have no type. While untyped variables have some drawbacks, they
have many more advantages and fit well with ruby's quick and
easy philosophy.
Variables must be declared in most languages in order to specify
their type, modifiability (i.e., whether they are constants), and
scope; since type is not an issue, and the rest is evident from the
variable name as you are about to see, we do not need variable
declarations in ruby.
The first character of an identifier categorizes it at a glance:
$ | global variable |
@ | instance variable |
[a-z] or _ | local variable |
[A-Z] | constant |
The only exceptions to the above are ruby's pseudo-variables:
self, which always refers to the currently executing
object, and nil, which is the meaningless value assigned
to uninitialized variables. Both are named as if they are local
variables, but self is a global variable maintained by
the interpreter, and nil is really a constant. As
these are the only two exceptions, they don't confuse things too
much.
You man not assign values to self or nil. main, as a
value of self, refers to the top-level object:
ruby> self
main
ruby> nil
nil |
