Penlight Documentation

# Module `pl.class`

Provides a reuseable and convenient framework for creating classes in Lua.

Two possible notations:

    B = class(A)
    class.B(A)

The latter form creates a named class within the current environment. Note that this implicitly brings in pl.utils as a dependency.

See the Guide for further discussion

## Functions

_init (...) | initializes an instance upon creation.
instance:is_a (some_class) | checks whether an instance is derived from some class.
some_class:class_of (some_instance) | checks whether an instance is derived from some class.
some_class:cast (some_instance) | cast an object to another class.
class (base, c_arg, c) | create a new class, derived from a given base class.

## Functions

_init (...)
  initializes an instance upon creation.

  ### Parameters:

  - ... parameters passed to the constructor

  ### Usage:

      local Cat = class()
      function Cat:_init(name)
        --self:super(name)   -- call the ancestor initializer if needed
        self.name = name
      end

      local pussycat = Cat("pussycat")
      print(pussycat.name)  --> pussycat

instance:is_a (some_class)
  checks whether an instance is derived from some class. Works the other way around as class_of. It has two ways of using; 1) call with a class to check against, 2) call without params.

  ### Parameters:

  - some_class class to check against, or `nil` to return the class

  ### Returns:

  `true` if `instance` is derived from `some_class`, or if `some_class == nil` then it returns the class table of the instance

  ### Usage:

      local pussycat = Lion()  -- assuming Lion derives from Cat
      if pussycat:is_a(Cat) then
        -- it's true, it is a Lion, but also a Cat
      end

      if pussycat:is_a() == Lion then
        -- It's true
      end

some_class:class_of (some_instance)
  checks whether an instance is derived from some class. Works the other way around as is_a.

  ### Parameters:

  - some_instance instance to check against

  ### Returns:

  `true` if `some_instance` is derived from `some_class`

  ### Usage:

      local pussycat = Lion()  -- assuming Lion derives from Cat
      if Cat:class_of(pussycat) then
        -- it's true
      end

some_class:cast (some_instance)
  cast an object to another class. It is not clever (or safe!) so use carefully.

  ### Parameters:

  - some_instance the object to be changed
class (base, c_arg, c)
  create a new class, derived from a given base class. Supporting two class creation syntaxes: either `Name = class(base)` or `class.Name(base)`. The first form returns the class directly and does not set its `_name`. The second form creates a variable `Name` in the current environment set to the class, and also sets `_name`.

  ### Parameters:

  - base optional base class
  - c_arg optional parameter to class constructor
  - c optional table to be used as class

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