うん、実装（ってかインタフェース）も書かれてていい感じ。
@_frozen public enum Result<Value, Error: Swift.Error> { case value(Value) case error(Error) public func map<NewValue>( _ transform: (Value) -> NewValue ) -> Result<NewValue, Error> public func mapError<NewError>( _ transform: (Error) -> NewError ) -> Result<Value, NewError> public func flatMap<NewValue>( _ transform: (Value) -> Result<NewValue, Error> ) -> Result<NewValue, Error> public func flatMapError<NewError>( _ transform: (Error) -> Result<Value, NewError> ) -> Result<Value, NewError> public func unwrapped() throws -> Value } extension Result where Error == Swift.Error { @_transparent public init(catching body: () throws -> Value) } extension Result : Equatable where Value : Equatable, Error : Equatable { } extension Result : Hashable where Value : Hashable, Error : Hashable { }