of an interface type or of elements of a composite type remains unchanged:
</p>

<pre>
// A Mutex is a data type with two methods, Lock and Unlock.
type Mutex struct         { /* Mutex fields */ }
func (m *Mutex) Lock()    { /* Lock implementation */ }
func (m *Mutex) Unlock()  { /* Unlock implementation */ }

// NewMutex has the same composition as Mutex but its method set is empty.

## 0.30.1

* Add section in docs about [External Links and Articles](https://fastapi.tiangolo.com/external-links/). PR [#341](https://github.com/tiangolo/fastapi/pull/341).

* Remove `Pipfile.lock` from the repository as it is only used by FastAPI contributors (developers of FastAPI itself). See the PR for more details. PR [#340](https://github.com/tiangolo/fastapi/pull/340).