feat: generic identifier (#27)

examples/example.rs

@@ -25,16 +25,26 @@ impl<'a> App<'a> {
     fn new() -> Self {
         Self {
             tree: StatefulTree::with_items(vec![
-                TreeItem::new_leaf("a"),
+                TreeItem::new_leaf("a", "Alfa"),
                 TreeItem::new(
                     "b",
+                    "Bravo",
                     vec![
-                        TreeItem::new_leaf("c"),
-                        TreeItem::new("d", vec![TreeItem::new_leaf("e"), TreeItem::new_leaf("f")]),
-                        TreeItem::new_leaf("g"),
+                        TreeItem::new_leaf("c", "Charlie"),
+                        TreeItem::new(
+                            "d",
+                            "Delta",
+                            vec![
+                                TreeItem::new_leaf("e", "Echo"),
+                                TreeItem::new_leaf("f", "Foxtrot"),
+                            ],
+                        )
+                        .expect("all item identifiers are unique"),
+                        TreeItem::new_leaf("g", "Golf"),
                     ],
-                ),
-                TreeItem::new_leaf("h"),
+                )
+                .expect("all item identifiers are unique"),
+                TreeItem::new_leaf("h", "Hotel"),
             ]),
         }
     }
@@ -74,6 +84,7 @@ fn run_app<B: Backend>(terminal: &mut Terminal<B>, mut app: App) -> io::Result<(
             let area = f.size();
 
             let items = Tree::new(app.tree.items.clone())
+                .expect("all item identifiers are unique")
                 .block(
                     Block::new()
                         .borders(Borders::ALL)

examples/util/mod.rs

@@ -1,8 +1,8 @@
 use tui_tree_widget::{TreeItem, TreeState};
 
 pub struct StatefulTree<'a> {
-    pub state: TreeState,
-    pub items: Vec<TreeItem<'a>>,
+    pub state: TreeState<&'static str>,
+    pub items: Vec<TreeItem<'a, &'static str>>,
 }
 
 impl<'a> StatefulTree<'a> {
@@ -14,7 +14,7 @@ impl<'a> StatefulTree<'a> {
         }
     }
 
-    pub fn with_items(items: Vec<TreeItem<'a>>) -> Self {
+    pub fn with_items(items: Vec<TreeItem<'a, &'static str>>) -> Self {
         Self {
             state: TreeState::default(),
             items,
@@ -22,7 +22,7 @@ impl<'a> StatefulTree<'a> {
     }
 
     pub fn first(&mut self) {
-        self.state.select_first();
+        self.state.select_first(&self.items);
     }
 
     pub fn last(&mut self) {