refactor: Avoid unneeded allocations (#1345)

examples/block.rs

@@ -14,7 +14,6 @@
 //! [examples readme]: https://github.com/ratatui/ratatui/blob/main/examples/README.md
 
 use color_eyre::Result;
-use itertools::Itertools;
 use ratatui::{
     crossterm::event::{self, Event, KeyCode, KeyEventKind},
     layout::{Alignment, Constraint, Layout, Rect},
@@ -90,7 +89,7 @@ fn calculate_layout(area: Rect) -> (Rect, Vec<Vec<Rect>>) {
                 .split(area)
                 .to_vec()
         })
-        .collect_vec();
+        .collect();
     (title_area, main_areas)
 }
 

examples/colors.rs

@@ -99,19 +99,16 @@ fn render_fg_named_colors(frame: &mut Frame, bg: Color, area: Rect) {
     let inner = block.inner(area);
     frame.render_widget(block, area);
 
-    let layout = Layout::vertical([Constraint::Length(1); 2])
+    let vertical = Layout::vertical([Constraint::Length(1); 2]).split(inner);
-        .split(inner)
+    let areas = vertical.iter().flat_map(|area| {
-        .iter()
+        Layout::horizontal([Constraint::Ratio(1, 8); 8])
-        .flat_map(|area| {
+            .split(*area)
-            Layout::horizontal([Constraint::Ratio(1, 8); 8])
+            .to_vec()
-                .split(*area)
+    });
-                .to_vec()
+    for (fg, area) in NAMED_COLORS.into_iter().zip(areas) {
-        })
-        .collect_vec();
-    for (i, &fg) in NAMED_COLORS.iter().enumerate() {
         let color_name = fg.to_string();
         let paragraph = Paragraph::new(color_name).fg(fg).bg(bg);
-        frame.render_widget(paragraph, layout[i]);
+        frame.render_widget(paragraph, area);
     }
 }
 
@@ -120,19 +117,16 @@ fn render_bg_named_colors(frame: &mut Frame, fg: Color, area: Rect) {
     let inner = block.inner(area);
     frame.render_widget(block, area);
 
-    let layout = Layout::vertical([Constraint::Length(1); 2])
+    let vertical = Layout::vertical([Constraint::Length(1); 2]).split(inner);
-        .split(inner)
+    let areas = vertical.iter().flat_map(|area| {
-        .iter()
+        Layout::horizontal([Constraint::Ratio(1, 8); 8])
-        .flat_map(|area| {
+            .split(*area)
-            Layout::horizontal([Constraint::Ratio(1, 8); 8])
+            .to_vec()
-                .split(*area)
+    });
-                .to_vec()
+    for (bg, area) in NAMED_COLORS.into_iter().zip(areas) {
-        })
-        .collect_vec();
-    for (i, &bg) in NAMED_COLORS.iter().enumerate() {
         let color_name = bg.to_string();
         let paragraph = Paragraph::new(color_name).fg(fg).bg(bg);
-        frame.render_widget(paragraph, layout[i]);
+        frame.render_widget(paragraph, area);
     }
 }
 

examples/constraint-explorer.rs

@@ -346,13 +346,8 @@ impl App {
     }
 
     fn render_user_constraints_legend(&self, area: Rect, buf: &mut Buffer) {
-        let blocks = Layout::horizontal(
+        let constraints = self.constraints.iter().map(|_| Constraint::Fill(1));
-            self.constraints
+        let blocks = Layout::horizontal(constraints).split(area);
-                .iter()
-                .map(|_| Constraint::Fill(1))
-                .collect_vec(),
-        )
-        .split(area);
 
         for (i, (area, constraint)) in blocks.iter().zip(self.constraints.iter()).enumerate() {
             let selected = self.selected_index == i;

examples/demo2/tabs/email.rs

@@ -96,13 +96,10 @@ fn render_inbox(selected_index: usize, area: Rect, buf: &mut Buffer) {
         .map(|e| e.from.width())
         .max()
         .unwrap_or_default();
-    let items = EMAILS
+    let items = EMAILS.iter().map(|e| {
-        .iter()
+        let from = format!("{:width$}", e.from, width = from_width).into();
-        .map(|e| {
+        ListItem::new(Line::from(vec![from, " ".into(), e.subject.into()]))
-            let from = format!("{:width$}", e.from, width = from_width).into();
+    });
-            ListItem::new(Line::from(vec![from, " ".into(), e.subject.into()]))
-        })
-        .collect_vec();
     let mut state = ListState::default().with_selected(Some(selected_index));
     StatefulWidget::render(
         List::new(items)

examples/demo2/tabs/traceroute.rs

@@ -52,10 +52,7 @@ impl Widget for TracerouteTab {
 
 fn render_hops(selected_row: usize, area: Rect, buf: &mut Buffer) {
     let mut state = TableState::default().with_selected(Some(selected_row));
-    let rows = HOPS
+    let rows = HOPS.iter().map(|hop| Row::new(vec![hop.host, hop.address]));
-        .iter()
-        .map(|hop| Row::new(vec![hop.host, hop.address]))
-        .collect_vec();
     let block = Block::new()
         .padding(Padding::new(1, 1, 1, 1))
         .title_alignment(Alignment::Center)

examples/layout.rs

@@ -74,31 +74,28 @@ fn draw(frame: &mut Frame) {
         Min(0), // fills remaining space
     ])
     .split(examples_area);
-    let example_areas = example_rows
+    let example_areas = example_rows.iter().flat_map(|area| {
+        Layout::horizontal([
+            Length(14),
+            Length(14),
+            Length(14),
+            Length(14),
+            Length(14),
+            Min(0), // fills remaining space
+        ])
+        .split(*area)
         .iter()
-        .flat_map(|area| {
+        .copied()
-            Layout::horizontal([
+        .take(5) // ignore Min(0)
-                Length(14),
+        .collect_vec()
-                Length(14),
+    });
-                Length(14),
-                Length(14),
-                Length(14),
-                Min(0), // fills remaining space
-            ])
-            .split(*area)
-            .iter()
-            .copied()
-            .take(5) // ignore Min(0)
-            .collect_vec()
-        })
-        .collect_vec();
 
     // the examples are a cartesian product of the following constraints
     // e.g. Len/Len, Len/Min, Len/Max, Len/Perc, Len/Ratio, Min/Len, Min/Min, ...
     let examples = [
         (
             "Len",
-            vec![
+            [
                 Length(0),
                 Length(2),
                 Length(3),
@@ -107,17 +104,11 @@ fn draw(frame: &mut Frame) {
                 Length(15),
             ],
         ),
-        (
+        ("Min", [Min(0), Min(2), Min(3), Min(6), Min(10), Min(15)]),
-            "Min",
+        ("Max", [Max(0), Max(2), Max(3), Max(6), Max(10), Max(15)]),
-            vec![Min(0), Min(2), Min(3), Min(6), Min(10), Min(15)],
-        ),
-        (
-            "Max",
-            vec![Max(0), Max(2), Max(3), Max(6), Max(10), Max(15)],
-        ),
         (
             "Perc",
-            vec![
+            [
                 Percentage(0),
                 Percentage(25),
                 Percentage(50),
@@ -128,7 +119,7 @@ fn draw(frame: &mut Frame) {
         ),
         (
             "Ratio",
-            vec![
+            [
                 Ratio(0, 4),
                 Ratio(1, 4),
                 Ratio(2, 4),
@@ -139,24 +130,15 @@ fn draw(frame: &mut Frame) {
         ),
     ];
 
-    for (i, (a, b)) in examples
+    for ((a, b), area) in examples
         .iter()
         .cartesian_product(examples.iter())
-        .enumerate()
+        .zip(example_areas)
     {
         let (name_a, examples_a) = a;
         let (name_b, examples_b) = b;
-        let constraints = examples_a
+        let constraints = examples_a.iter().copied().zip(examples_b.iter().copied());
-            .iter()
+        render_example_combination(frame, area, &format!("{name_a}/{name_b}"), constraints);
-            .copied()
-            .zip(examples_b.iter().copied())
-            .collect_vec();
-        render_example_combination(
-            frame,
-            example_areas[i],
-            &format!("{name_a}/{name_b}"),
-            constraints,
-        );
     }
 }
 
@@ -165,7 +147,7 @@ fn render_example_combination(
     frame: &mut Frame,
     area: Rect,
     title: &str,
-    constraints: Vec<(Constraint, Constraint)>,
+    constraints: impl ExactSizeIterator<Item = (Constraint, Constraint)>,
 ) {
     let block = Block::bordered()
         .title(title.gray())
@@ -174,8 +156,8 @@ fn render_example_combination(
     let inner = block.inner(area);
     frame.render_widget(block, area);
     let layout = Layout::vertical(vec![Length(1); constraints.len() + 1]).split(inner);
-    for (i, (a, b)) in constraints.into_iter().enumerate() {
+    for ((a, b), &area) in constraints.into_iter().zip(layout.iter()) {
-        render_single_example(frame, layout[i], vec![a, b, Min(0)]);
+        render_single_example(frame, area, vec![a, b, Min(0)]);
     }
     // This is to make it easy to visually see the alignment of the examples
     // with the constraints.

examples/table.rs

@@ -294,7 +294,7 @@ fn generate_fake_names() -> Vec<Data> {
             }
         })
         .sorted_by(|a, b| a.name.cmp(&b.name))
-        .collect_vec()
+        .collect()
 }
 
 fn constraint_len_calculator(items: &[Data]) -> (u16, u16, u16) {

src/layout/constraint.rs

@@ -1,6 +1,5 @@
 use std::fmt;
 
-use itertools::Itertools;
 use strum::EnumIs;
 
 /// A constraint that defines the size of a layout element.
@@ -229,7 +228,7 @@ impl Constraint {
     where
         T: IntoIterator<Item = u16>,
     {
-        lengths.into_iter().map(Self::Length).collect_vec()
+        lengths.into_iter().map(Self::Length).collect()
     }
 
     /// Convert an iterator of ratios into a vector of constraints
@@ -246,10 +245,7 @@ impl Constraint {
     where
         T: IntoIterator<Item = (u32, u32)>,
     {
-        ratios
+        ratios.into_iter().map(|(n, d)| Self::Ratio(n, d)).collect()
-            .into_iter()
-            .map(|(n, d)| Self::Ratio(n, d))
-            .collect_vec()
     }
 
     /// Convert an iterator of percentages into a vector of constraints
@@ -266,7 +262,7 @@ impl Constraint {
     where
         T: IntoIterator<Item = u16>,
     {
-        percentages.into_iter().map(Self::Percentage).collect_vec()
+        percentages.into_iter().map(Self::Percentage).collect()
     }
 
     /// Convert an iterator of maxes into a vector of constraints
@@ -283,7 +279,7 @@ impl Constraint {
     where
         T: IntoIterator<Item = u16>,
     {
-        maxes.into_iter().map(Self::Max).collect_vec()
+        maxes.into_iter().map(Self::Max).collect()
     }
 
     /// Convert an iterator of mins into a vector of constraints
@@ -300,7 +296,7 @@ impl Constraint {
     where
         T: IntoIterator<Item = u16>,
     {
-        mins.into_iter().map(Self::Min).collect_vec()
+        mins.into_iter().map(Self::Min).collect()
     }
 
     /// Convert an iterator of proportional factors into a vector of constraints
@@ -317,10 +313,7 @@ impl Constraint {
     where
         T: IntoIterator<Item = u16>,
     {
-        proportional_factors
+        proportional_factors.into_iter().map(Self::Fill).collect()
-            .into_iter()
-            .map(Self::Fill)
-            .collect_vec()
     }
 }
 

src/layout/layout.rs

@@ -1315,9 +1315,9 @@ mod tests {
                 .flex(flex)
                 .split(area);
             let mut buffer = Buffer::empty(area);
-            for (i, c) in ('a'..='z').take(constraints.len()).enumerate() {
+            for (c, &area) in ('a'..='z').take(constraints.len()).zip(layout.iter()) {
                 let s = c.to_string().repeat(area.width as usize);
-                Paragraph::new(s).render(layout[i], &mut buffer);
+                Paragraph::new(s).render(area, &mut buffer);
             }
             assert_eq!(buffer, Buffer::with_lines([expected]));
         }

src/text/text.rs

@@ -1,8 +1,6 @@
 #![warn(missing_docs)]
 use std::{borrow::Cow, fmt};
 
-use itertools::{Itertools, Position};
-
 use crate::{prelude::*, style::Styled};
 
 /// A string split over one or more lines.
@@ -632,12 +630,11 @@ impl<T: fmt::Display> ToText for T {
 
 impl fmt::Display for Text<'_> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        for (position, line) in self.iter().with_position() {
+        if let Some((last, rest)) = self.lines.split_last() {
-            if position == Position::Last || position == Position::Only {
+            for line in rest {
-                write!(f, "{line}")?;
-            } else {
                 writeln!(f, "{line}")?;
             }
+            write!(f, "{last}")?;
         }
         Ok(())
     }