text: // Copyright 2020 The Druid Authors.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  //! Support for lenses, a way of focusing on subfields of data.
  //!
  //! Lenses are useful whenever a widget only needs access to a subfield of a larger struct or
  //! generally access to part of a larger value.
  //!
  //! For example: If one wants to embed a [`TextBox`] in a widget with a `Data` type
  //! that is not `String`, they need to specify how to access a `String` from within the `Data`.
  //!
  //! [`TextBox`]: ../widget/struct.TextBox.html
  //! ```
  //! use druid::{Data, Lens, Widget, WidgetExt, widget::{TextBox, Flex}};
  //!
  //! #[derive(Clone, Debug, Data, Lens)]
  //! struct MyState {
  //!     search_term: String,
  //!     scale: f64,
  //!     // ...
  //! }
  //!
  //!
  //! fn my_sidebar() -> impl Widget<MyState> {
  //!     // `TextBox` is of type `Widget<String>`
  //!     // via `.lens` we get it to be of type `Widget<MyState>`.
  //!     // `MyState::search_term` is a lens generated by the `derive(Lens)` macro,
  //!     // that provides access to the search_term field.
  //!     let searchbar = TextBox::new().lens(MyState::search_term);
  //!
  //!     // ...
  //!
  //!     // We can now use `searchbar` just like any other `Widget<MyState>`
  //!     Flex::column().with_child(searchbar)
  //! }
  //! ```
  
  #[allow(clippy::module_inception)]
  mod lens;
  pub use lens::{Deref, Field, Id, InArc, Index, Map, Ref, Then, Unit};
  #[doc(hidden)]
  pub use lens::{Lens, LensExt};
  