91 lines
2.7 KiB
Swift
Executable File
91 lines
2.7 KiB
Swift
Executable File
/// A property wrapper that tracks changes of a property.
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///
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/// This allows values to only publish changes if they have changed since the
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/// last time they were recieved.
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@propertyWrapper
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public struct TrackedChanges<Value> {
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/// The current tracking state.
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private var tracking: TrackingState
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/// The current wrapped value.
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private var value: Value
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/// Used to check if a new value is equal to an old value.
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private var isEqual: (Value, Value) -> Bool
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/// Access to the underlying property that we are wrapping.
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public var wrappedValue: Value {
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get { value }
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set {
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// Check if the new value is equal to the old value.
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guard !isEqual(newValue, value) else { return }
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// If it's not equal then set it, as well as set the tracking to `.needsProcessed`.
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value = newValue
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tracking = .needsProcessed
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}
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}
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/// Create a new property that tracks it's changes.
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///
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/// - Parameters:
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/// - wrappedValue: The value that we are wrapping.
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/// - needsProcessed: Whether this value needs processed (default = false).
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/// - isEqual: Method to compare old values against new values.
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public init(
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wrappedValue: Value,
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needsProcessed: Bool = false,
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isEqual: @escaping (Value, Value) -> Bool
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) {
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self.value = wrappedValue
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self.tracking = needsProcessed ? .needsProcessed : .hasProcessed
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self.isEqual = isEqual
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}
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/// Represents whether a wrapped value has changed and needs processed or not.
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enum TrackingState {
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/// The state when nothing has changed and we've already processed the current value.
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case hasProcessed
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/// The state when the value has changed and has not been processed yet.
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case needsProcessed
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}
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/// Check whether the value needs processed.
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public var needsProcessed: Bool {
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get { tracking == .needsProcessed }
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set {
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if newValue {
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tracking = .needsProcessed
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} else {
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tracking = .hasProcessed
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}
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}
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}
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public var projectedValue: Self {
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get { self }
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set { self = newValue }
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}
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}
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extension TrackedChanges: Equatable where Value: Equatable {
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public static func == (lhs: TrackedChanges<Value>, rhs: TrackedChanges<Value>) -> Bool {
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lhs.wrappedValue == rhs.wrappedValue
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&& lhs.needsProcessed == rhs.needsProcessed
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}
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/// Create a new property that tracks it's changes, using the default equality check.
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///
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/// - Parameters:
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/// - wrappedValue: The value that we are wrapping.
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/// - needsProcessed: Whether this value needs processed (default = false).
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public init(
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wrappedValue: Value,
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needsProcessed: Bool = false
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) {
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self.init(wrappedValue: wrappedValue, needsProcessed: needsProcessed, isEqual: ==)
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}
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}
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