An exploration of a possible KVC-like API for a future version of Swift.

swift-kvc.swift

/// A statically typed view into a get-only property.
struct TypedGetPropertyView<T> {
	/// The name of the property, as a string.
	let name : String
	
	/// The actual metatype of the property.
	let metatype : T.Type
	
	/// Get the value of the property.
	func get() -> T
	
	/// Attempt to build a statically typed view from a dynamically typed view.
	init?(propertyView: GetPropertyView)
}

/// A statically typed view into a get-set property.
struct TypedGetSetPropertyView<T> {
	let name : String
	let metatype : T.Type
	func get() -> T
	
	/// Set the property to a new value.
	func set(newValue: T)
	
	init?(propertyView: GetSetPropertyView)
	
	/// If a get-only view corresponds to a get-set property, return a new
	/// view that allows for getting and setting of the value.
	init?(propertyView: TypedGetPropertyView<T>)
}

/// A dynamically typed view into a get-only property.
struct GetPropertyView {
	let name : String
	let metatype : Any.Type
	func get() -> Any
	
	/// Turn a statically typed view into a dynamic view.
	init<T>(propertyView: GetPropertyView<T>)
}

/// A dynamically typed view into a get-set property.
struct GetSetPropertyView {
	let name : String
	let metatype : Any.Type
	func get() -> Any
	
	/// Attempt to set the property to a new value. Throws if a type error occurs.
	func set(newValue: Any) throws
	
	init<T>(propertyView: GetSetPropertyView<T>)
	
	init?(propertyView: GetPropertyView<T>)
}

/// Either a statically typed get-only property, or a get-set property.
enum TypedPropertyView<T> {
	case Get(TypedGetPropertyView<T>)
	case GetSet(TypedGetSetPropertyView<T>)
	
	var asGet : TypedGetPropertyView<T>?
	var asGetSet : TypedGetSetPropertyView<T>?
}

/// Either a dynamically typed get-only property, or a get-set property.
enum PropertyView {
	case Get(GetPropertyView)
	case GetSet(GetSetPropertyView)
	
	var asGet : GetPropertyView?
	var asGetSet : GetSetPropertyView?
}

/// Conform a type to PropertyReflectable for the compiler to automatically generate
/// an interface for reflecting upon properties. 
@magic protocol PropertyReflectable {

	/// Returns an untyped view into a property with a given name, or nil if no property
	/// with that name exists.
	func property(name: String, searchSupertype: Bool = false) -> PropertyView?
	
	/// Returns a get-only view into a property with a given name, or nil if no property
	/// with that name exists.
	func getOnlyProperty(name: String, searchSupertype: Bool = false) -> GetPropertyView?
	
	/// Returns a get-set view into a property with a given name, or nil if the property
	/// either doesn't exist or is a get-only property.
	func getSetProperty(name: String, searchSupertype: Bool = false) -> GetSetPropertyView?

	/// Returns a typed view into a property with a given name, or nil if no property
	/// with the given name and type exists. If the property's type is a subtype of
	/// the given type, a view into the property parameterized by the given type will
	/// be returned.
	func typedProperty<T>(name: String, searchSupertype: Bool = false) -> TypedPropertyView<T>?

	/// Returns a typed get-only view into a property with a given name. Returns nil if no
	/// property with the name exists or the type is incompatible.
	func typedGetOnlyProperty<T>(name: String, searchSupertype: Bool = false) -> TypedGetPropertyView<T>?
	
	/// Returns a typed get-set view into a property with a given name. Returns nil if no
	/// property with the naame exists, the type is incompatible, or the property is get-only.
	func typedGetSetProperty(name: String, searchSupertype: Bool = false) -> TypedGetSetPropertyView<T>?

	/// Returns an array of untyped views into each of the properties defined on this
	/// type.
	func allProperties(includeSupertypeProperties: Bool = false) -> [PropertyView]
	
	/// Returns a dictionary of untyped views into each of the properties defined on
	/// this type. The keys are the property names; the values are the views.
	func allNamedProperties(includeSupertypeProperties: Bool = false) -> [String : PropertyView]
}