More fixes to get rid of implicit Display

Add an explicit DisplayModel

NEWS.md

@@ -2,7 +2,7 @@
 
 ## Unreleased
 
-- **Breaking change:** `Render` no longer has a blanket implementation for `Display`: you can no longer use a string, integer, or some object that implements `Display` as a model directly. You must instead implement `Render` explicitly.
+- **Breaking change:** `Render` no longer has a blanket implementation for `Display`: you can no longer use a string, integer, or some object that implements `Display` as a model directly. You can instead implement `Render` explicitly, or opt in to this behavior using the new `nutmeg::models::DisplayModel`.
 
   It seems that the `Display` implementation is often not a very satisfactory progress bar, and the presence of the blanket implementation causes confusing error messages when `Render` is not implemented correctly.
 

examples/bench.rs

@@ -4,15 +4,23 @@
 
 use std::time::Instant;
 
+struct IntModel(usize);
+
+impl nutmeg::Model for IntModel {
+    fn render(&mut self, _width: usize) -> String {
+        format!("count: {}", self.0)
+    }
+}
+
 fn main() {
     let start = Instant::now();
-    let view = nutmeg::View::new(0u64, nutmeg::Options::default());
+    let view = nutmeg::View::new(IntModel(0), nutmeg::Options::default());
     let n = 10_000_000;
     for i in 0..n {
-        view.update(|model| *model = i);
+        view.update(|IntModel(count)| *count = i);
     }
     view.message(format!(
-        "{}ms to send {} updates; average {}ns/update",
+        "{}ms to send {} updates; average {}ns/update\n",
         start.elapsed().as_millis(),
         n,
         start.elapsed().as_nanos() / n as u128,

examples/print_holdoff.rs

@@ -11,22 +11,24 @@ use std::thread;
 use std::time;
 use std::time::Duration;
 
+use nutmeg::models::LinearModel;
+
 fn main() -> io::Result<()> {
     let options = nutmeg::Options::default()
         .print_holdoff(Duration::from_millis(1000))
         .update_interval(Duration::from_millis(0));
-    let mut view = nutmeg::View::new(0usize, options);
+    let mut view = nutmeg::View::new(LinearModel::new("Things", 50), options);
     for _i in 0..5 {
         for j in 0..4 {
             writeln!(view, "message {j}")?;
             thread::sleep(time::Duration::from_millis(100));
         }
         for j in 0..20 {
-            view.update(|state| {
+            view.update(|model| {
                 // Previous updates were applied even though
                 // they may not have been painted.
-                assert!(j == 0 || *state == (j - 1));
-                *state = j
+                assert!(j == 0 || model.done() == (j - 1));
+                model.set_done(j);
             });
             thread::sleep(time::Duration::from_millis(100));
         }

src/lib.rs

@@ -487,10 +487,13 @@ impl<M: Model> View<M> {
     ///
     /// ```
     /// use nutmeg::{Options, View};
+    /// use nutmeg::models::LinearModel;
     ///
-    /// let view = View::new(10, Options::default());
-    /// view.update(|model| *model += 3);
-    /// assert_eq!(view.inspect_model(|m| *m), 13);
+    /// let mut model = LinearModel::new("Things done", 100);
+    /// model.set_done(10);
+    /// let view = View::new(model, Options::default());
+    /// view.update(|model| model.increment(3));
+    /// assert_eq!(view.inspect_model(|m| m.done()), 13);
     /// ```
     pub fn inspect_model<F, R>(&self, f: F) -> R
     where
@@ -524,10 +527,15 @@ impl<M: Model> View<M> {
     ///
     /// ```
     /// use nutmeg::{Options, View};
+    /// use nutmeg::models::LinearModel;
     ///
-    /// let view = View::new(0, Options::default());
-    /// // ...
-    /// view.message(format!("{} splines reticulated\n", 42));
+    /// let view = View::new(LinearModel::new("Splines reticulated", 100), Options::default());
+    /// for i in 0..20 {
+    ///     view.update(|model| model.increment(1));
+    ///     if i == 12 {
+    ///         view.message("Some quality splines here!\n");
+    ///     }
+    /// }
     /// ```
     pub fn message<S: AsRef<str>>(&self, message: S) {
         self.message_bytes(message.as_ref().as_bytes())
@@ -541,8 +549,9 @@ impl<M: Model> View<M> {
     ///
     /// ```
     /// use nutmeg::{Options, View};
+    /// use nutmeg::models::LinearModel;
     ///
-    /// let view = View::new("model content", Options::default());
+    /// let view = View::new(LinearModel::new("Things done", 100), Options::default());
     /// view.message_bytes(b"hello crow\n");
     /// ```
     pub fn message_bytes<S: AsRef<[u8]>>(&self, message: S) {
@@ -563,8 +572,11 @@ impl<M: Model> View<M> {
     ///
     /// ```
     /// use nutmeg::{Destination, Options, View};
+    /// use nutmeg::models::DisplayModel;
     ///
-    /// let view = View::new(0, Options::default().destination(Destination::Capture));
+    /// let view = View::new(
+    ///     DisplayModel("unchanging message"),
+    ///     Options::default().destination(Destination::Capture));
     /// let output = view.captured_output();
     /// view.message("Captured message\n");
     /// drop(view);

src/models.rs

@@ -7,6 +7,7 @@
 //! requirement to use them: they only implement the public [Model] interface.
 
 use std::borrow::Cow;
+use std::fmt::{Debug, Display};
 use std::time::{Duration, Instant};
 
 #[allow(unused)] // For docstrings
@@ -86,6 +87,7 @@ impl Model for StringPair {
 ///     progress.update(|model| model.increment(1));
 /// }
 /// ```
+#[derive(Debug)]
 pub struct LinearModel {
     done: usize,
     total: usize,
@@ -109,6 +111,16 @@ impl LinearModel {
         self.total = total
     }
 
+    /// Get the total number of things.
+    pub fn total(&self) -> usize {
+        self.total
+    }
+
+    /// Get the number of things done so far.
+    pub fn done(&self) -> usize {
+        self.done
+    }
+
     /// Update the amount of work done.
     ///
     /// This should normally be called from a callback passed to [View::update].
@@ -270,3 +282,13 @@ where
         (self.render_fn)(&mut self.value)
     }
 }
+
+/// A model that holds a single value and renders it using its `Display` implementation.
+#[derive(Debug)]
+pub struct DisplayModel<T: Display + Debug>(pub T);
+
+impl<T: Display + Debug> Model for DisplayModel<T> {
+    fn render(&mut self, _width: usize) -> String {
+        format!("{}", self.0)
+    }
+}

tests/captured_in_tests.rs

@@ -11,19 +11,21 @@
 
 use std::io::Write;
 
+use nutmeg::models::DisplayModel;
+
 #[test]
 fn view_stdout_captured() {
-    let mut view = nutmeg::View::new(String::new(), nutmeg::Options::default());
-    view.update(|model| *model = "stdout progress should be captured".into());
+    let mut view = nutmeg::View::new(DisplayModel("hello"), nutmeg::Options::default());
+    view.update(|DisplayModel(message)| *message = "stdout progress should be captured");
     writeln!(view, "stdout message should be captured").unwrap();
 }
 
 #[test]
 fn view_stderr_captured() {
     let mut view = nutmeg::View::new(
-        String::new(),
+        DisplayModel("initial"),
         nutmeg::Options::default().destination(nutmeg::Destination::Stderr),
     );
-    view.update(|model| *model = "stderr progress should be captured".into());
+    view.update(|model| model.0 = "stderr progress should be captured");
     writeln!(view, "stderr message should be captured").unwrap();
 }