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Rust

Domain modeling, influenced by functional programming principles, aims to represent the business domain in the code accurately. Rust is ideal thanks to its ownership model and type system, which enforce correctness and reliability - enabling you to eliminate many classes of bugs at compile-time, guarantying memory-safety and thread-safety.

Decide​

type DecideFunction<'a, C, S, E> = Box<dyn Fn(&C, &S) -> Vec<E> + 'a + Send + Sync>

On a higher level of abstraction, any information system is responsible for handling the intent (Command) and based on the current State, produce new facts (Events):

  • given the current State/S on the input,
  • when Command/C is handled on the input,
  • expect Vec of new Events/E to be published/emitted on the output

Evolve​

type EvolveFunction<'a, S, E> = Box<dyn Fn(&S, &E) -> S + 'a + Send + Sync>

The new state is always evolved out of the current state S and the current event E:

  • given the current State/S on the input,
  • when Event/E is handled on the input,
  • expect new State/S to be published on the output

Two functions are wrapped in a datatype class (algebraic data structure), which is generalized with three generic parameters:

pub struct Decider<'a, C: 'a, S: 'a, E: 'a> {
    pub decide: DecideFunction<'a, C, S, E>,
    pub evolve: EvolveFunction<'a, S, E>,
    pub initial_state: InitialStateFunction<'a, S>,
}

Further reading​

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