user itertools join to avoid allocations

Author: benmkw

gitoxide-core/src/hours/util.rs

@@ -42,6 +42,29 @@ impl<'a> From<&'a WorkByEmail> for WorkByPerson {
     }
 }
 
+fn join<I>(mut iter: I, sep: &str) -> String
+where
+    I: Iterator,
+    <I as Iterator>::Item: std::fmt::Display,
+{
+    use ::std::fmt::Write;
+
+    match iter.next() {
+        None => String::new(),
+        Some(first_elt) => {
+            // estimate lower bound of capacity needed
+            let (lower, _) = iter.size_hint();
+            let mut result = String::with_capacity(sep.len() * lower);
+            write!(&mut result, "{first_elt}").unwrap();
+            iter.for_each(|elt| {
+                result.push_str(sep);
+                write!(&mut result, "{elt}").unwrap();
+            });
+            result
+        }
+    }
+}
+
 impl WorkByPerson {
     pub fn write_to(
         &self,
@@ -53,22 +76,8 @@ impl WorkByPerson {
         writeln!(
             out,
             "{names} <{mails}>",
-            names = self
-                .name
-                .iter()
-                // BStr does not impl slice::Join
-                .map(|s| s.to_string())
-                .collect::<Vec<_>>()
-                .as_slice()
-                .join(", "),
-            mails = self
-                .email
-                .iter()
-                // BStr does not impl slice::Join
-                .map(|s| s.to_string())
-                .collect::<Vec<_>>()
-                .as_slice()
-                .join(", ")
+            names = join(self.name.iter(), ", "),
+            mails = join(self.email.iter(), ", ")
         )?;
         writeln!(out, "{} commits found", self.num_commits)?;
         writeln!(