Object-Oriented Programming (OOP)

Rhai does not have objects per se, but it is possible to simulate object-oriented programming.

Use Object Maps to Simulate OOP

Rhai’s object maps has special support for OOP.

When a property of an object map is called like a method function, and if it happens to hold a valid function pointer (perhaps defined via an anonymous function or more commonly as a closure), then the call will be dispatched to the actual function with this binding to the object map itself.

Use Closures to Define Methods

Anonymous functions or closures defined as values for object map properties take on a syntactic shape which resembles very closely that of class methods in an OOP language.

Closures also capture variables from the defining environment, which is a very common language feature. Capturing is accomplished via a feature called automatic currying and can be turned off via the no_closure feature.

Examples

#![allow(unused)]
fn main() {
let factor = 1;

// Define the object
let obj = #{
        data: 0,                             // object field
        increment: |x| this.data += x,       // 'this' binds to 'obj'
        update: |x| this.data = x * factor,  // 'this' binds to 'obj', 'factor' is captured
        action: || print(this.data)          // 'this' binds to 'obj'
    };

// Use the object
obj.increment(1);
obj.action();                                // prints 1

obj.update(42);
obj.action();                                // prints 42

factor = 2;

obj.update(42);
obj.action();                                // prints 84
}

Simulating Inheritance With Mixin

The fill_with method of object maps can be conveniently used to polyfill default method implementations from a base class, as per OOP lingo.

Do not use the mixin method because it overwrites existing fields.

#![allow(unused)]
fn main() {
// Define base class
let BaseClass = #{
    factor: 1,
    data: 42,

    get_data: || this.data * 2,
    update: |x| this.data += x * this.factor
};

let obj = #{
    // Override base class field
    factor: 100,

    // Override base class method
    // Notice that the base class can also be accessed, if in scope
    get_data: || this.call(BaseClass.get_data) * 999,
}

// Polyfill missing fields/methods
obj.fill_with(BaseClass);

// By this point, 'obj' has the following:
//
// #{
//      factor: 100
//      data: 42,
//      get_data: || this.call(BaseClass.get_data) * 999,
//      update: |x| this.data += x * this.factor
// }

// obj.get_data() => (this.data (42) * 2) * 999
obj.get_data() == 83916;

obj.update(1);

obj.data == 142
}