Add Button::dynamic constructor

CHANGELOG.md

@@ -48,6 +48,7 @@ This means that druid no longer requires cairo on macOS and uses Core Graphics i
 - `im` feature, with `Data` support for the [`im` crate](https://docs.rs/im/) collections. ([#924] by [@cmyr])
 - `im::Vector` support for the `List` widget. ([#940] by [@xStrom])
 - `LifeCycle::Size` event to inform widgets that their size changed. ([#953] by [@xStrom])
+- `Button::dynamic` constructor. ([#963] by [@totsteps])
 
 ### Changed
 
@@ -204,6 +205,7 @@ This means that druid no longer requires cairo on macOS and uses Core Graphics i
 [#954]: https://github.com/xi-editor/druid/pull/954
 [#959]: https://github.com/xi-editor/druid/pull/959
 [#961]: https://github.com/xi-editor/druid/pull/961
+[#963]: https://github.com/xi-editor/druid/pull/963
 
 ## [0.5.0] - 2020-04-01
 

druid/src/widget/button.rs

@@ -52,6 +52,31 @@ impl<T: Data> Button<T> {
         }
     }
 
+    /// Construct a new dynamic button.
+    ///
+    /// The contents of this button are generated from the data using a closure.
+    ///
+    /// This is provided as a convenience; a closure can also be passed to [`new`],
+    /// but due to limitations of the implementation of that method, the types in
+    /// the closure need to be annotated, which is not true for this method.
+    ///
+    /// # Examples
+    ///
+    /// The following are equivalent.
+    ///
+    /// ```
+    /// use druid::Env;
+    /// use druid::widget::Button;
+    /// let button1: Button<u32> = Button::new(|data: &u32, _: &Env| format!("total is {}", data));
+    /// let button2: Button<u32> = Button::dynamic(|data, _| format!("total is {}", data));
+    /// ```
+    ///
+    /// [`new`]: #method.new
+    pub fn dynamic(text: impl Fn(&T, &Env) -> String + 'static) -> Self {
+        let text: LabelText<T> = text.into();
+        Button::new(text)
+    }
+
     /// Provide a closure to be called when this button is clicked.
     pub fn on_click(
         self,

druid/src/widget/label.rs

@@ -104,8 +104,8 @@ impl<T: Data> Label<T> {
     /// ```
     /// use druid::Env;
     /// use druid::widget::Label;
-    /// let button1: Label<u32> = Label::new(|data: &u32, _: &Env| format!("total is {}", data));
-    /// let button2: Label<u32> = Label::dynamic(|data, _| format!("total is {}", data));
+    /// let label1: Label<u32> = Label::new(|data: &u32, _: &Env| format!("total is {}", data));
+    /// let label2: Label<u32> = Label::dynamic(|data, _| format!("total is {}", data));
     /// ```
     ///
     /// [`new`]: #method.new