Comparison of class variables and instance variables in Ruby, ruby class variable instances

Source: Internet
Author: User

Comparison of class variables and instance variables in Ruby, ruby class variable instances

1. The class variable name starts with @. A Class variable is shared by all instance objects of the class. The instance variable name starts with @, and each instance object has its own different instance variables;

2. class variables must be initialized before use; otherwise, an error is reported during use. If the instance variables are not initialized, nil is returned during use;

3. class variables are private and cannot be directly accessed outside the class. They can be accessed through class methods and instance methods;

Copy codeThe Code is as follows:
Class B
@ Number = 11
@ Num = 22
 
Def my_method # define the instance method
Puts @ number
End
 
Def self. my_method # define class methods
Puts @ num
End
End
 
B = B. new ()
Puts B. my_method () # variables of the sort class through the instance method => 11
Puts B. my_method () # Use the class method variables => 22

4. instance variables are private and cannot be directly referenced outside the class. They can be accessed through class methods and instance methods;

Copy codeThe Code is as follows:
Class B
@ Num = 11 # This is actually "instance variable of the class"
@ Test = 22
Def my_method # define the instance method
Puts @ num = 33 # It is not in the same scope as @ num defined above => 33
Puts @ test # It is not in the same scope as the @ test defined above, and no initial value is assigned. Therefore, nil is returned.
Puts @ new = 567 # instance variables defined only when the instance runs my_method => 567
End
Def self. my_method # define class methods
Puts @ num # Here @ num is the previously defined @ num => 11
Puts @ test # => 22
End
End

B = B. new ()

B. my_method
Puts "--------------------"
B. my_method

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