Classes

The Lua language does not have a built-in class construct. However, the Renoise Lua API provides simple object-oriented programming support via a global class() function. All Renoise API objects use such classes, and you can use them in your tools as well.

See the luabind documentation for more technical information, and the examples below for how to use them.

Examples

-- abstract class
class 'Animal'

  function Animal:__init(name)
    self.name = name
    self.can_fly = nil
  end  

  function Animal:__tostring()
    assert(self.can_fly ~= nil, "I don't know if I can fly or not")
    
    return ("I am a %s (%s) and I %s"):format(self.name, type(self), 
      (self.can_fly and "can fly" or "cannot fly"))
  end


-- derived classes

-- MAMMAL
class 'Mammal' (Animal)

  function Mammal:__init(str)
    Animal.__init(self, str)
    self.can_fly = false
  end

-- BIRD
class 'Bird' (Animal)

  function Bird:__init(str)
    Animal.__init(self, str)
    self.can_fly = true
  end

-- FISH
class 'Fish' (Animal)

  function Fish:__init(str)
    Animal.__init(self, str)
    self.can_fly = false
  end


-- run

local farm = {}

table.insert(farm, Mammal("cow"))
table.insert(farm, Bird("sparrow"))
table.insert(farm, Fish("bass"))

print(("type(Mammal('cow')) -> %s"):format(type(Mammal("cow"))))
print(("type(Mammal) -> %s"):format(type(Mammal)))

for _,animal in ipairs(farm) do
  print(animal)
end

Something to keep in mind:

• A constructor, function MyClass:__init(args), must be defined for each class, or the class cannot be used to instantiate objects.
• Class definitions are always global, so even locally defined classes will be registered globally.

Class operators

You can overload most operators in Lua for your classes. You do this by simply declaring a member function with the same name as an operator's corresponding metamethod in Lua.

The operators you can overload are:

• __add (addition)
• __sub (subtraction)
• __mul (multiplication)
• __div (division)
• __pow (exponentiation)
• __lt (less than)
• __le (less than or equal to)
• __eq (equality)
• __call (function call)
• __unm (unary minus)
• __tostring (serialization)
• __len (length operator #)

Note: __tostring isn't really an operator, but it's the metamethod that is called by the standard library's tostring() function.