Struct relm4::shared_state::Reducer

pub struct Reducer<Data: Reducible> { /* private fields */ }

A type that allows you to share information across your application easily.

Reducers receive messages, update their state accordingly and notify their subscribers.

Unlike SharedState, this type doesn’t allow direct access to the internal data. Instead, it updates its state after receiving messages, similar to components. After the message is processed, all subscribers will be notified.

Example

use relm4::{Reducer, Reducible};

struct CounterReducer(u8);

enum CounterInput {
    Increment,
    Decrement,
}

impl Reducible for CounterReducer {
    type Input = CounterInput;

    fn init() -> Self {
        Self(0)
    }

    fn reduce(&mut self, input: Self::Input) -> bool {
        match input {
            CounterInput::Increment => {
                self.0 += 1;
            }
            CounterInput::Decrement =>  {
                self.0 -= 1;
            }
        }
        true
    }
}

// Create the reducer.
static REDUCER: Reducer<CounterReducer> = Reducer::new();

// Update the reducer.
REDUCER.emit(CounterInput::Increment);

// Create a channel and subscribe to changes.
let (sender, receiver) = relm4::channel();
REDUCER.subscribe(&sender, |data| data.0);

// Count up to 2.
REDUCER.emit(CounterInput::Increment);
assert_eq!(receiver.recv_sync().unwrap(), 2);

Implementations

impl<Data> Reducer<Data>

where Data: Reducible + Send + 'static, Data::Input: Send,

pub const fn new() -> Self

Create a new Reducer variable.

The data will be initialized lazily on the first access.

pub fn subscribe<Msg, F>(&self, sender: &Sender<Msg>, f: F)

where F: Fn(&Data) -> Msg + 'static + Send + Sync, Msg: Send + 'static,

Subscribe to a Reducer. Any subscriber will be notified with a message every time you modify the reducer (by calling Self::emit()).

pub fn subscribe_optional<Msg, F>(&self, sender: &Sender<Msg>, f: F)

where F: Fn(&Data) -> Option<Msg> + 'static + Send + Sync, Msg: Send + 'static,

An alternative version of subscribe() that only send a message if the closure returns Some.

pub fn emit(&self, input: Data::Input)

Sends a message to the reducer to update its state.

If the Reducible::reduce() method returns true, all subscribers will be notified.

Trait Implementations

impl<Data: Debug + Reducible> Debug for Reducer<Data>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<Data> Default for Reducer<Data>

where Data: Reducible + Send + 'static, Data::Input: Send,

fn default() -> Self

Returns the “default value” for a type.