Member Variable

In object-oriented programming, a member variable (sometimes called a member field) is a variable that is associated with a specific object, and accessible for all its methods (''member functions'').

In class-based programming languages, these are distinguished into two types: '' class variables'' (also called ''static member variables''), where only one copy of the variable is shared with all instances of the class; and '' instance variables'', where each instance of the class has its own independent copy of the variable.

Examples

C++

class Foo ;

int main ()

Java

public class Program

public class Foo

Python

class Foo:
def __init__(self):
self._bar = 0

@property
def bar(self):
return self._bar

@bar.setter
def bar(self, new_bar):
self._bar = new_bar

f = Foo()
f.bar = 100
print(f.bar)

Common Lisp

(defclass foo () (bar))

(defvar f (make-instance 'foo))
(setf (slot-value f 'bar) 100)
(print (slot-value f 'bar))

Ruby

/*
Ruby has three member variable types: class, class instance, and instance.
*/

class Dog

# The class variable is defined within the class body with two at-signs
# and describes data about all Dogs *and* their derived Dog breeds (if any)
@@sniffs = true

end

mutt = Dog.new
mutt.class.sniffs #=> true

class Poodle < Dog

# The "class instance variable" is defined within the class body with a single at-sign
# and describes data about only the Poodle class. It makes no claim about its parent class
# or any possible subclass derived from Poodle
@sheds = false

# When a new Poodle instance is created, by default it is untrained. The 'trained' variable
# is local to the initialize method and is used to set the instance variable @trained
# An instance variable is defined within an instance method and is a member of the Poodle instance
def initialize(trained = false)
@trained = trained
end

def has_manners?
@trained
end

end

p = Poodle.new
p.class.sheds #=> false
p.has_manners? #=> false

PHP

foo = 10;

// Prints 10.
echo $example->foo;

Lua

--region example
--- @class example_c
--- @field foo number Example "member variable".
local example_c =
local example_mt =

--- Creates an object from example.
--- @return example_c
function example_c.new(foo)
-- The first table argument is our object's member variables.
-- In a Lua object is a metatable and its member variables are table key-value pairs.
return setmetatable(, example_mt)
end
--endregion

-- Create an example object.
-- Set the "foo" member variable to 5.
local example = example_c.new(5)

-- Overwrite the "foo" member variable to 10.
example.foo = 10

-- Prints 10.
print(example.foo)

See also

* Global variable
* Local variable
* Property (programming)

References

{{Reflist

Object-oriented programming
Variable (computer science)
Articles with example Python (programming language) code