From 71ed45ee584fc345775ccdd44770b584f4c1d1c7 Mon Sep 17 00:00:00 2001
From: Michael Hordijk <hordijk@aurora.tech>
Date: Mon, 5 Feb 2024 15:30:16 -0700
Subject: [PATCH] add comment regarding use of unary `+` operator

---
 au/io.hh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/au/io.hh b/au/io.hh
index 26c8165c..f52464ff 100644
--- a/au/io.hh
+++ b/au/io.hh
@@ -25,6 +25,11 @@ namespace au {
 // Streaming output support for Quantity types.
 template <typename U, typename R>
 std::ostream &operator<<(std::ostream &out, const Quantity<U, R> &q) {
+    // In the case that the Rep is a type that resolves to 'char' (e.g. int8_t),
+    // the << operator will match the implementation that takes a character
+    // literal.  Using the unary + operator will trigger an integer promotion on
+    // the operand, which will then match an appropriate << operator that will
+    // output the integer representation.
     out << +q.in(U{}) << " " << unit_label(U{});
     return out;
 }