Ruby Language Variable Scope and Visibility Global Variables
Example
Global variables have a global scope and hence, can be used everywhere. Their scope is not dependent on where they are defined. A variable will be considered global, when prefixed with a $ sign.
$i_am_global = "omg"
class Dinosaur
def instance_method
p "global vars can be used everywhere. See? #{$i_am_global}, #{$another_global_var}"
end
def self.class_method
$another_global_var = "srsly?"
p "global vars can be used everywhere. See? #{$i_am_global}"
end
end
Dinosaur.class_method
# "global vars can be used everywhere. See? omg"
# => "global vars can be used everywhere. See? omg"
dinosaur = Dinosaur.new
dinosaur.instance_method
# "global vars can be used everywhere. See? omg, srsly?"
# => "global vars can be used everywhere. See? omg, srsly?"
Since a global variable can be defined everywhere and will be visible everywhere, calling an "undefined" global variable will return nil instead of raising an error.
p $undefined_var
# nil
# => nil
Although global variables are easy to use its usage is strongly discouraged in favour of constants.
