Ruby Learning: Global Variables and constants

First, global variables

Global variables are supported in Ruby, and global variables in Ruby are characterized by the following:

1) identifiers are marked with a $ start

2) Global variables can be referenced from anywhere in the program

3) nil.

Let's take a look at the example

 class   Demo  def   puts $a end end puts $a  #   reference undeclared global variable, $a this value is nil  demo  = Demo.newdemo.   print  #    $a  =12demo.   print  #   The output is 12 because then $ A already has a value of  

It should be explained that in the actual coding we try not to define global variables, using global variables is a very bad way of programming.

Second, constant

Constants in Ruby must be defined in a class and cannot be defined in a method, and the first letter of a constant identifier must be capitalized.

Example:

class Demo     = 3.14        defprint        puts Pi    end    End    # Create an object, call the method of the object = Demo.newdemo .  Print  = 4  # There will be a warning, but there will be no error, and the modification will take effect demo. Print

Note that it is different from other languages. The value of a constant can be modified outside the class (it cannot be modified in the method of the Class), although a warning is reported, but no error occurs.

Ruby Learning: Global Variables and constants