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// 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.
//! Implementations of [`Lens`], 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`](crate::widget::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`.
//!
//! ```
//! 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)
//! }
//! ```
//!
//! Most of the time, if you want to create your own lenses, you need to use
//! [`#[derive(Lens)]`](druid_derive::Lens).
#[allow(clippy::module_inception)]
#[macro_use]
mod lens;
pub use lens::{
Constant, Deref, Field, Identity, InArc, Index, Lens, LensExt, Map, Ref, Then, Unit,
};