For some types which "wrap" other values, the constructor may wrap its argument inside a new object even if it is already of the requested type. For example Some(x) wraps x to indicate that a value is present (in a context where the result might be a Some or nothing). However, x itself might be the object Some(y), in which case the result is Some(Some(y)), with two levels of wrapping. convert(Some, x), on the other hand, would just return x since it is already a Some.