Classes and objects

A Koskari class is a Python class. Methods are callable from Python, Python decorators apply, and instances are ordinary objects.

Defining

Python

class Point:
    """A point in 2D space"""
    x: int = 0
    y: int = 0

Koskari

class Point []:
  """ A point in 2D space """
  var x :: int 0
  var y :: int 0

What is the []?

The base list. Empty means no explicit base, as class Point: does. class Child (Parent): subclasses. The :: carries an annotation, and it lands in __annotations__ as the real type object.

Methods

Python

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def coord(self):
        return (self.x, self.y)

Koskari

class Point []:
  def __init__ [self x y]:
    set! self.x x
    set! self.y y

  def coord [self]:
    #(self.x self.y)

Is self special?

No more than in Python. It is the first formal, by convention named self. self.x reads the attribute and set! self.x writes it; dunder methods follow Python’s rules because the class is a Python type.

Properties

Python

class Circle:
    _radius = 0.0

    @property
    def radius(self):
        return self._radius

    @radius.setter
    def radius(self, value):
        self._radius = float(value)

Koskari

class Circle []:
  var _radius :: float 0.0

  @property
  def radius [self]:
    self._radius

  @radius.setter
  def radius [self value]:
    set! self._radius (float value)

Does property need @demand?

No. Koskari’s property wraps a Koskari accessor for the demand path itself, so a getter, setter, and deleter are plain def forms.

Python decorators

Python

from dataclasses import dataclass

@dataclass
class Point:
    x: int = 0
    y: int = 0

p = Point(3, 5)

Koskari

import-from dataclasses dataclass

@dataclass
class Point []:
  var x :: int 0
  var y :: int 0

var p (Point 3 5)

Which decorators work?

Any importable callable, above class or above a method. The class body’s annotated var forms are what dataclass reads, so it generates __init__, __repr__, and __eq__ as it would for the Python spelling.

Instances

Python

p = Point(3, 5)
isinstance(p, Point)
p.x

Koskari

var p (Point 3 5)
(instance? p Point)
p.x

Can Python code use the class?

Yes. Import the .ki module from Python and Point is a normal type, with isinstance, dataclasses.fields, and everything else that works on one.

Run it

Save as point.ki:

import-from dataclasses dataclass

@dataclass
class Point []:
  var x :: int 0
  var y :: int 0

  def label [self]:
    f"Point at ({self.x}, {self.y})"

@entry-point
def main []:
  var p (Point 1 2)
  print (p.label)
  print p

Point at (1, 2)
Point(x=1, y=2)

A larger version with a generator method and a property is the Point class example.