add iter_join helper method to more efficiently join string vecs

src/utils.rs

@@ -0,0 +1,31 @@
+/// Lovingly borrowed from the cargo crate
+///
+/// Joins an iterator of [std::fmt::Display]'ables into an output writable
+pub(crate) fn iter_join_onto<W, I, T>(mut w: W, iter: I, delim: &str) -> std::fmt::Result
+where
+    W: std::fmt::Write,
+    I: IntoIterator<Item = T>,
+    T: std::fmt::Display,
+{
+    let mut it = iter.into_iter().peekable();
+    while let Some(n) = it.next() {
+        write!(w, "{}", n)?;
+        if it.peek().is_some() {
+            write!(w, "{}", delim)?;
+        }
+    }
+    Ok(())
+}
+
+/// Lovingly borrowed from the cargo crate
+///
+/// Joins an iterator of [std::fmt::Display]'ables to a new [std::string::String].
+pub(crate) fn iter_join<I, T>(iter: I, delim: &str) -> String
+where
+    I: IntoIterator<Item = T>,
+    T: std::fmt::Display,
+{
+    let mut s = String::new();
+    let _ = iter_join_onto(&mut s, iter, delim);
+    s
+}