Support returning errors when creating the app (#4565)

The closure passed to `eframe::run_native` now returns a `Result`,
allowing you to return an error during app creation, which will be
returned to the caller of `run_native`.

This means you need to wrap your `Box::new(MyApp::new(…))` in an
`Ok(…)`.

* Closes https://github.com/emilk/egui/issues/4474

examples/confirm_exit/src/main.rs

@@ -12,7 +12,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Confirm exit",
         options,
-        Box::new(|_cc| Box::<MyApp>::default()),
+        Box::new(|_cc| Ok(Box::<MyApp>::default())),
     )
 }
 

examples/custom_3d_glow/src/main.rs

@@ -19,7 +19,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Custom 3D painting in eframe using glow",
         options,
-        Box::new(|cc| Box::new(MyApp::new(cc))),
+        Box::new(|cc| Ok(Box::new(MyApp::new(cc)))),
     )
 }
 

examples/custom_font/src/main.rs

@@ -12,7 +12,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "egui example: custom font",
         options,
-        Box::new(|cc| Box::new(MyApp::new(cc))),
+        Box::new(|cc| Ok(Box::new(MyApp::new(cc)))),
     )
 }
 

examples/custom_font_style/src/main.rs

@@ -11,7 +11,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "egui example: global font style",
         options,
-        Box::new(|cc| Box::new(MyApp::new(cc))),
+        Box::new(|cc| Ok(Box::new(MyApp::new(cc)))),
     )
 }
 

examples/custom_keypad/src/main.rs

@@ -20,7 +20,7 @@ fn main() -> Result<(), eframe::Error> {
             // This gives us image support:
             egui_extras::install_image_loaders(&cc.egui_ctx);
 
-            Box::<MyApp>::default()
+            Ok(Box::<MyApp>::default())
         }),
     )
 }

examples/custom_plot_manipulation/src/main.rs

@@ -11,7 +11,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Plot",
         options,
-        Box::new(|_cc| Box::<PlotExample>::default()),
+        Box::new(|_cc| Ok(Box::<PlotExample>::default())),
     )
 }
 

examples/custom_window_frame/src/main.rs

@@ -19,7 +19,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Custom window frame", // unused title
         options,
-        Box::new(|_cc| Box::<MyApp>::default()),
+        Box::new(|_cc| Ok(Box::<MyApp>::default())),
     )
 }
 

examples/file_dialog/src/main.rs

@@ -14,7 +14,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Native file dialogs and drag-and-drop files",
         options,
-        Box::new(|_cc| Box::<MyApp>::default()),
+        Box::new(|_cc| Ok(Box::<MyApp>::default())),
     )
 }
 

examples/hello_world/src/main.rs

@@ -16,7 +16,7 @@ fn main() -> Result<(), eframe::Error> {
             // This gives us image support:
             egui_extras::install_image_loaders(&cc.egui_ctx);
 
-            Box::<MyApp>::default()
+            Ok(Box::<MyApp>::default())
         }),
     )
 }

examples/hello_world_par/src/main.rs

@@ -17,7 +17,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "My parallel egui App",
         options,
-        Box::new(|_cc| Box::new(MyApp::new())),
+        Box::new(|_cc| Ok(Box::new(MyApp::new()))),
     )
 }
 

examples/images/src/main.rs

@@ -15,7 +15,7 @@ fn main() -> Result<(), eframe::Error> {
         Box::new(|cc| {
             // This gives us image support:
             egui_extras::install_image_loaders(&cc.egui_ctx);
-            Box::<MyApp>::default()
+            Ok(Box::<MyApp>::default())
         }),
     )
 }

examples/keyboard_events/src/main.rs

@@ -10,7 +10,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Keyboard events",
         options,
-        Box::new(|_cc| Box::<Content>::default()),
+        Box::new(|_cc| Ok(Box::<Content>::default())),
     )
 }
 

examples/multiple_viewports/src/main.rs

@@ -17,7 +17,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Multiple viewports",
         options,
-        Box::new(|_cc| Box::<MyApp>::default()),
+        Box::new(|_cc| Ok(Box::<MyApp>::default())),
     )
 }
 

examples/puffin_profiler/src/main.rs

@@ -22,7 +22,7 @@ fn main() -> Result<(), eframe::Error> {
 
             ..Default::default()
         },
-        Box::new(|_cc| Box::<MyApp>::default()),
+        Box::new(|_cc| Ok(Box::<MyApp>::default())),
     )
 }
 

examples/save_plot/src/main.rs

@@ -14,7 +14,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "My egui App with a plot",
         options,
-        Box::new(|_cc| Box::<MyApp>::default()),
+        Box::new(|_cc| Ok(Box::<MyApp>::default())),
     )
 }
 

examples/screenshot/src/main.rs

@@ -14,7 +14,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Take screenshots and display with eframe/egui",
         options,
-        Box::new(|_cc| Box::<MyApp>::default()),
+        Box::new(|_cc| Ok(Box::<MyApp>::default())),
     )
 }
 

examples/serial_windows/src/main.rs

@@ -23,7 +23,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "First Window",
         options.clone(),
-        Box::new(|_cc| Box::new(MyApp { has_next: true })),
+        Box::new(|_cc| Ok(Box::new(MyApp { has_next: true }))),
     )?;
 
     std::thread::sleep(std::time::Duration::from_secs(2));
@@ -32,7 +32,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Second Window",
         options.clone(),
-        Box::new(|_cc| Box::new(MyApp { has_next: true })),
+        Box::new(|_cc| Ok(Box::new(MyApp { has_next: true }))),
     )?;
 
     std::thread::sleep(std::time::Duration::from_secs(2));
@@ -41,7 +41,7 @@ fn main() -> Result<(), eframe::Error> {
     eframe::run_native(
         "Third Window",
         options,
-        Box::new(|_cc| Box::new(MyApp { has_next: false })),
+        Box::new(|_cc| Ok(Box::new(MyApp { has_next: false }))),
     )
 }
 

examples/user_attention/src/main.rs

@@ -15,7 +15,7 @@ fn main() -> eframe::Result<()> {
     eframe::run_native(
         "User attention test",
         native_options,
-        Box::new(|cc| Box::new(Application::new(cc))),
+        Box::new(|cc| Ok(Box::new(Application::new(cc)))),
     )
 }