Isolated State - Swift Programming

Concurrent programs keep mutable state behind a small boundary.

Update through one boundary

isolated_state.swift

struct CounterState {
    var value = 0

    mutating func add(_ amount: Int) {
        value += amount
    }
}

let amount = 
var state = CounterState()
state.add(amount)
let message = "counter=\(state.value)"

print(message)

struct CounterState {
    var value = 0

    mutating func add(_ amount: Int) {
        value += amount
    }
}

let amount = 
var state = CounterState()
state.add(amount)
let message = "counter=\(state.value)"

print(message)

struct CounterState {
    var value = 0

    mutating func add(_ amount: Int) {
        value += amount
    }
}

let amount = 
var state = CounterState()
state.add(amount)
let message = "counter=\(state.value)"

print(message)

isolated state This small type models the same idea actors enforce: callers update state through a method instead of changing storage from many places.