Problem Statement

In object-oriented programming class is a set (a transitive closure) of types bound by the relation of inheritance. It is said that all types derived from some base type T and the type T itself form a class T. The first type T from the class T sometimes is called the root type of the class. A class of types itself, as a type, has the values and operations of its own. The operations of are usually called methods of the root type. Both operations and values are called polymorphic. A polymorphic operation (method) selects an implementation depending on the actual specific type of the polymorphic argument. The action of choice the type-specific implementation of a polymorphic operation is called dispatch. Correspondingly, polymorphic operations are often called dispatching or virtual. Operations with multiple arguments and/or the results of the class are called multi-methods. A further generalization of is the operation with arguments and/or results from different classes.

A polymorphic value has a type tag indicating its specific type from the class and the corresponding specific value of that type. This type is sometimes called the most specific type of a [polymorphic] value. The type tag of the value is used in order to resolve the dispatch. The set of polymorphic values of a class is a transitive closure of the sets of values of all types from that class. In many OO languages the type of the class of T and T itself are considered equivalent. In some languages they are distinct (like in Ada). When class T and T are equivalent, there is no way to distinguish polymorphic and specific values.

Create a basic class with a method, a constructor, an instance variable and how to instantiate it.

Let's start with the solution:

struct MyClass {
    variable: i32, // member variable = instance variable
}

impl MyClass {
    // member function = method, with its implementation
    fn some_method(&mut self) {
        self.variable = 1;
    }

    // constructor, with its implementation
    fn new() -> MyClass {
        // Here could be more code.
        MyClass { variable: 0 }
    }
}

fn main () {
    // Create an instance in the stack.
    let mut instance = MyClass::new();

    // Create an instance in the heap.
    let mut p_instance = Box::new(MyClass::new());

    // Invoke method on both istances,
    instance.some_method();
    p_instance.some_method();

    // Both instances are automatically deleted when their scope ends.
}