Func Modules: Modularizing Behavior

Func modules separate behavior from entities, making Flint entities highly modular. They act upon data and can be reused across multiple entities. A func module defines functionality independently of a specific entity.

Syntax Recap:

data CounterData:
    int value = 0;
    CounterData(value);

func CounterActions requires(CounterData c);
    def increment(int amount):
        c.value += amount;

    def get_value() -> int:
        return c.value;

Key Points:

1. Requires Keyword: The requires keyword specifies the data module(s) this func module operates on. In this case, it requires a data module of type Counter. This data module has to be present on every entity that uses the CounterActions func module.
2. Reusability: A single func module can be shared across multiple entities that use compatible data structures.
3. Immutability: Just like with monolithic entities, the data saved inside an entity cannot be accessed outside of func modules. So, when Entity E uses a func module which acts on data D the data of D cannot be accessed via an instance of E. This means that e.value is impossible. For all operations on data, getters and setters must be provided inside the func module.

By separating behavior from data, Flint encourages reuse and cleaner code. But how do these fit into entities?