A collection of macros which add class support to Nim. To install, run nimble install classes. Features include:
- Simple class syntax
- Class variables with default values
- Inheritance and
super.calls() - Default constructors
- Static and abstract methods
- Methods and variables defined in any order
- Mixins
import classes
# A base class
class Shape:
## The position of the shape
var x = 0
var y = 0
## Optional constructor
method init() =
echo "Creating a Shape"
## Optional destructor (not supported in JS)
method deinit() =
echo "Destroying a Shape"
## Abstract draw function
method draw()
## Calculate size
method calculateSize(): float = return 0
## Static method
method defaultSize(): float {.static.} = 5
# A subclass
class Square of Shape:
# Radius
var radius = 5
## Override constructor
method init() =
super.init()
echo "Creating a Square"
## Draw it
method draw() =
echo "Drawing a square of size " & $this.calculateSize()
## Calculate size
method calculateSize(): float = super.calculateSize() + this.radius
# Many ways of creating class instances:
let obj = Square.init()
let obj = Square().init()
let obj = newSquare()
# Call static methods
# NOTE: Static methods don't always work if the name of your nim file is the exact same as the class name.
# You may get a `type mismatch: got <>` error in that case.
Shape.defaultSize()
# Data only classes
class DataOnly:
var v0 = 7
var v1: int
var v2: string
# Constructing it this way allows you to pass in values for the variables that don't have values set
let obj = DataOnly(v1: 10, v2: "20").init()
# Using the mixin keyword will copy the variables and methods from one class to another
class CustomNote:
var note = ""
class Circle of Shape:
mixin CustomNote
let circle = Circle.init()
circle.note = "My custom note"
# Singleton classes act the same way as standard classes, but use a .shared() accessor instead of constructors.
# The default constructor is called the first time the singleton class is accessed.
singleton MySingletonClass:
var v1 = 7
method init() = echo "Singleton accessed for the first time!"
# Access the singleton, this also triggers the init() the first time
echo MySingletonClass.shared.v1- JS backend: As of Nim 1.4.8 (when I last tested), the internal dom library is exposing a
class()function, and this function always takes precedent over this library'sclassmacro. I don't know how to fix this. In the mean time, you can replace the wordclasswithclasses.class
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