Rust Patterns in Swift.md

Just trying to see how Rust patterns work in Swift

Type State Machine.swift

// from: https://doc.rust-lang.org/beta/embedded-book/static-guarantees/design-contracts.html#type-states

protocol EnabledState {}
protocol DirectionState {}
protocol ModeState {}

struct GpioConfig<IsEnabled: EnabledState, Direction: DirectionState, Mode: ModeState> {
    var periph: Int64

    init(periph: Int64) {
        self.periph = periph
    }
}

struct Disabled: EnabledState {}
struct Enabled: EnabledState {}
struct Output: DirectionState {}
struct Input: DirectionState {}
struct PulledLow: ModeState {}
struct PulledHigh: ModeState {}
struct HighZ: ModeState {}
struct DontCare: EnabledState, ModeState, DirectionState {}

/// These functions may be used on any GPIO Pin
extension GpioConfig {
    func into_disabled() -> GpioConfig<Disabled, DontCare, DontCare> {
        // periph modifications omitted
        .init(periph: periph)
    }

    func into_enabled_input() -> GpioConfig<Enabled, Input, HighZ> {
        // periph modifications omitted
        .init(periph: periph)
    }

    func into_enabled_output() -> GpioConfig<Enabled, Output, DontCare> {
        // periph modifications omitted
        .init(periph: periph)
    }
}

extension GpioConfig where IsEnabled == Enabled, Direction == Output, Mode == DontCare {
    mutating func set_bit(_ set_high: Bool) {
        // periph modifications omitted
    }
}

extension GpioConfig where IsEnabled == Enabled, Direction == Input {
    func bit_is_set() -> Bool {
        // periph read omitted
        true
    }

    func into_input_high_z() -> GpioConfig<Enabled, Input, HighZ> {
        // periph modifications omitted
        .init(periph: periph)
    }

    func into_input_pull_down() -> GpioConfig<Enabled, Input, PulledLow> {
        // periph modifications omitted
        .init(periph: periph)
    }

    func into_input_pull_up() -> GpioConfig<Enabled, Input, PulledHigh> {
        // periph modifications omitted
        .init(periph: periph)
    }
}

func get_gpio() -> GpioConfig<DontCare, DontCare, DontCare> {
    // periph code omitted
    .init(periph: 0)
}

/*
 * Example 1: Unconfigured to High-Z input
 */
let pin = get_gpio()

// Can't do this, pin isn't enabled!
// pin.into_input_pull_down();

// Now turn the pin from unconfigured to a high-z input
let input_pin = pin.into_enabled_input()

// Read from the pin
print("pin_state:", input_pin.bit_is_set())

// Can't do this, input pins don't have this interface!
// input_pin.set_bit(true)

/*
 * Example 2: High-Z input to Pulled Low input
 */
let pulled_low = input_pin.into_input_pull_down()
print("pin_state:", pulled_low.bit_is_set())

/*
 * Example 3: Pulled Low input to Output, set high
 */
var output_pin = pulled_low.into_enabled_output()
output_pin.set_bit(true)

// Can't do this, output pins don't have this interface!
// output_pin.into_input_pull_down()

print("size:", MemoryLayout.size(ofValue: output_pin)) // 8