Lua Study Notes 4: class and integration implementation

-- Implementation of classes in Lua


-------------------------------- Base class ----------------------------
Classbase = {x = 0, y = 0} -- X, Y is the member variable of the class.
Classbase. _ Index = classbase -- this statement is used to redefine the meta-Table index, which must have


-- Simulate the constructor, which is generally named new ()
Function classbase: New (x, y)
Local Self ={} -- initialize the object itself
Setretriable (self, classbase) -- must have
Self. x = x
Self. Y = y
Return self
End


Function classbase: Show () -- member function of the class
Print (self. X, self. Y)
End


-- Basic test code
Obja = classbase: New () -- call to create a class object for a function
Obja: Show () -- call class Method
Print (obja. X, obja. y) -- member variable of the struct class


-- # Lua allows you to add an additional parameter self in a method definition using a colon,
-- # In this way, an error is returned when calling sequence BJA. Show (). Self is nil.
-- # Print (obja: X, obja: Y) Error


-------------------------------- Inheritance: derived class ----------------------------
Classderived = {z = 0} -- add member variables
Setretriable (classderived, classbase) -- set the type to classbase.
Classderived. _ Index = classderived -- same as the class definition, the index value indicates itself.


-- Constructor
Function classderived: New (x, y, z)
Local Self = {}
Self = classbase: New (x, y) -- set the object itself as a parent class, which is equivalent to calling the constructor of the parent class.
Setretriable (self, classderived) -- set the object metadata table to classderived
Self. z = z -- new attribute initialization. If not, it will be declared as 0


Return self
End


-- Override the parent class Method
Function classderived: Show ()
Print (self. X, self. Y, self. Z)
End


-- Add Method
Function classderived: showsum ()
Print (self. x + self. Y + self. Z)
End


-- Test code of a derived class
Objb = classderived: New (, 3) -- call to create a Class Object
Objb: Show () -- call the rewrite method, reflecting Polymorphism
Objb: showsum () -- call the newly added Method