Elegant state machine for Swift.
enum MyState: StateType {
case state0, state1, state2
}// setup state machine
let machine = StateMachine<MyState, NoEvent>(state: .state0) { machine in
machine.addRoute(.state0 => .state1)
machine.addRoute(.any => .state2) { context in print("Any => 2, msg=\(context.userInfo)") }
machine.addRoute(.state2 => .any) { context in print("2 => Any, msg=\(context.userInfo)") }
// add handler (`context = (event, fromState, toState, userInfo)`)
machine.addHandler(.state0 => .state1) { context in
print("0 => 1")
}
// add errorHandler
machine.addErrorHandler { event, fromState, toState, userInfo in
print("[ERROR] \(fromState) => \(toState)")
}
}
// initial
XCTAssertEqual(machine.state, MyState.state0)
// tryState 0 => 1 => 2 => 1 => 0
machine <- .state1
XCTAssertEqual(machine.state, MyState.state1)
machine <- (.state2, "Hello")
XCTAssertEqual(machine.state, MyState.state2)
machine <- (.state1, "Bye")
XCTAssertEqual(machine.state, MyState.state1)
machine <- .state0 // fail: no 1 => 0
XCTAssertEqual(machine.state, MyState.state1)This will print:
0 => 1
Any => 2, msg=Optional("Hello")
2 => Any, msg=Optional("Bye")
[ERROR] state1 => state0Use <-! operator to try transition by Event rather than specifying target State.
enum MyEvent: EventType {
case event0, event1
}let machine = StateMachine<MyState, MyEvent>(state: .state0) { machine in
// add 0 => 1 => 2
machine.addRoutes(event: .event0, transitions: [
.state0 => .state1,
.state1 => .state2,
])
// add event handler
machine.addHandler(event: .event0) { context in
print(".event0 triggered!")
}
}
// initial
XCTAssertEqual(machine.state, MyState.state0)
// tryEvent
machine <-! .event0
XCTAssertEqual(machine.state, MyState.state1)
// tryEvent
machine <-! .event0
XCTAssertEqual(machine.state, MyState.state2)
// tryEvent (fails)
machine <-! .event0
XCTAssertEqual(machine.state, MyState.state2, "event0 doesn't have 2 => Any")If there is no Event-based transition, use built-in NoEvent instead.
Above examples use arrow-style routing which are easy to understand, but it lacks in ability to handle state & event enums with associated values. In such cases, use either of the following functions to apply closure-style routing:
machine.addRouteMapping(routeMapping)RouteMapping:(_ event: E?, _ fromState: S, _ userInfo: Any?) -> S?
machine.addStateRouteMapping(stateRouteMapping)StateRouteMapping:(_ fromState: S, _ userInfo: Any?) -> [S]?
For example:
enum StrState: StateType {
case str(String) ...
}
enum StrEvent: EventType {
case str(String) ...
}
let machine = Machine<StrState, StrEvent>(state: .str("initial")) { machine in
machine.addRouteMapping { event, fromState, userInfo -> StrState? in
// no route for no-event
guard let event = event else { return nil }
switch (event, fromState) {
case (.str("gogogo"), .str("initial")):
return .str("Phase 1")
case (.str("gogogo"), .str("Phase 1")):
return .str("Phase 2")
case (.str("finish"), .str("Phase 2")):
return .str("end")
default:
return nil
}
}
}
// initial
XCTAssertEqual(machine.state, StrState.str("initial"))
// tryEvent (fails)
machine <-! .str("go?")
XCTAssertEqual(machine.state, StrState.str("initial"), "No change.")
// tryEvent
machine <-! .str("gogogo")
XCTAssertEqual(machine.state, StrState.str("Phase 1"))
// tryEvent (fails)
machine <-! .str("finish")
XCTAssertEqual(machine.state, StrState.str("Phase 1"), "No change.")
// tryEvent
machine <-! .str("gogogo")
XCTAssertEqual(machine.state, StrState.str("Phase 2"))
// tryEvent (fails)
machine <-! .str("gogogo")
XCTAssertEqual(machine.state, StrState.str("Phase 2"), "No change.")
// tryEvent
machine <-! .str("finish")
XCTAssertEqual(machine.state, StrState.str("end"))This behaves very similar to JavaScript's safe state-container rackt/Redux, where RouteMapping can be interpretted as Redux.Reducer.
For more examples, please see XCTest cases.
- Easy Swift syntax
- Transition:
.state0 => .state1,[.state0, .state1] => .state2 - Try state:
machine <- .state1 - Try state + messaging:
machine <- (.state1, "GoGoGo") - Try event:
machine <-! .event1
- Transition:
- Highly flexible transition routing
-
Using
Condition -
Using
.anystate- Entry handling:
.any => .someState - Exit handling:
.someState => .any - Blacklisting:
.any => .any+Condition
- Entry handling:
-
Using
.anyevent -
Route Mapping (closure-based routing): #36
-
- Success/Error handlers with
order: UInt8(more flexible than before/after handlers) - Removable routes and handlers using
Disposable - Route Chaining:
.state0 => .state1 => .state2 - Hierarchical State Machine: #10
| Term | Type | Description |
|---|---|---|
| State | StateType (protocol) |
Mostly enum, describing each state e.g. .state0. |
| Event | EventType (protocol) |
Name for route-group. Transition can be fired via Event instead of explicitly targeting next State. |
| State Machine | Machine |
State transition manager which can register Route/RouteMapping and Handler separately for variety of transitions. |
| Transition | Transition |
From- and to- states represented as .state1 => .state2. Also, .any can be used to represent any state. |
| Route | Route |
Transition + Condition. |
| Condition | Context -> Bool |
Closure for validating transition. If condition returns false, transition will fail and associated handlers will not be invoked. |
| Route Mapping | (event: E?, fromState: S, userInfo: Any?) -> S? |
Another way of defining routes using closure instead of transition arrows (=>). This is useful when state & event are enum with associated values. Return value (S?) means preferred-toState, where passing nil means no routes available. See #36 for more info. |
| State Route Mapping | (fromState: S, userInfo: Any?) -> [S]? |
Another way of defining routes using closure instead of transition arrows (=>). This is useful when state is enum with associated values. Return value ([S]?) means multiple toStates from single fromState (synonym for multiple routing e.g. .state0 => [.state1, .state2]). See #36 for more info. |
| Handler | Context -> Void |
Transition callback invoked when state has been changed successfully. |
| Context | (event: E?, fromState: S, toState: S, userInfo: Any?) |
Closure argument for Condition & Handler. |
| Chain | TransitionChain / RouteChain |
Group of continuous routes represented as .state1 => .state2 => .state3 |
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