func withExtendedLifetime<T, Result>(_: T, _: T throws -> Result) Evaluate f(x) and return its result, ensuring that x is not destroyed before f returns. Declaration func withExtendedLifetime<T, Result>(x: T, @noescape _ f: T throws -> Result) rethrows -> Result func withExtendedLifetime<T, Result>(_: T, _: () throws -> Result) Evaluate f() and return its result, ensuring that x is not destroyed before f returns. Declaration func withExtendedLifetime<T, Result>(x: T, @noescape _ f: () throws -> Result) rethrows -> Result