# Special Support for OOP via Object Maps

Object maps can be used to simulate object-oriented programming (OOP) by storing data as properties and methods as properties holding function pointers.

If an object map‘s property holds a function pointer, the property can simply be called like a normal method in method-call syntax. This is a short-hand to avoid the more verbose syntax of using the call function keyword.

When a property holding a function pointer or a closure is called like a method, what happens next depends on whether the target function is a native Rust function or a script-defined function.

• If it is a registered native Rust function, it is called directly in method-call style with the object map inserted as the first argument.

• If it is a script-defined function, the this variable within the function body is bound to the object map before the function is called.


#![allow(unused)]
fn main() {
let obj = #{
data: 40,
action: || this.data += x    // 'action' holds a closure
};

obj.action(2);                               // calls the function pointer with this bound to 'obj'

obj.call(obj.action, 2);                     // <- the above de-sugars to this

obj.data == 42;

// To achieve the above with normal function pointer call will fail.
fn do_action(map, x) { map.data += x; }      // 'map' is a copy

obj.action = Fn("do_action");

obj.action.call(obj, 2);                     // 'obj' is passed as a copy by value
}