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_archive/rhai_engine/rhaibook/language/object-maps-oop.md

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+Special Support for OOP via Object Maps
+=======================================
+
+{{#include ../links.md}}
+
+```admonish info.side "See also"
+
+See the pattern on [_Simulating Object-Oriented Programming_][OOP] for more details.
+```
+
+[Object maps] can be used to simulate [object-oriented programming (OOP)][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, it is replaced
+as a method call on the [object map] itself.
+
+```rust
+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 = do_action;                      // <- de-sugars to 'Fn("do_action")'
+
+obj.action.call(obj, 2);                     // a copy of 'obj' is passed by value
+
+obj.data == 42;                              // 'obj.data' is not changed
+```