type HasFoo = concept v v.foo is string WithFoo = object foo: string WithoutFoo = object bar: string proc conceptual[T: HasFoo](val: T) = echo $(val.foo) proc general[T](val: T) = echo $(val.foo) var foo = WithFoo(foo:"foo") bar = WithoutFoo(bar:"bar") conceptual(foo) conceptual(bar) general(foo) general(bar)