2 files changed, 4 insertions, 4 deletions
diff --git a/src/openvic/Date.cpp b/src/openvic/Date.cpp
index 003a455..d25e99f 100644
--- a/src/openvic/Date.cpp
+++ b/src/openvic/Date.cpp
@@ -57,7 +57,7 @@ Timespan::operator std::string() const {
 	return std::to_string(days);
 }
 
-std::ostream& operator<<(std::ostream& out, Timespan timespan) {
+std::ostream& OpenVic::operator<<(std::ostream& out, Timespan const& timespan) {
 	return out << static_cast<std::string>(timespan);
 }
 
@@ -128,7 +128,7 @@ Date::operator std::string() const {
 	return ss.str();
 }
 
-std::ostream& operator<<(std::ostream& out, Date date) {
+std::ostream& OpenVic::operator<<(std::ostream& out, Date const& date) {
 	return out << (int) date.getYear() << '.' << (int) date.getMonth() << '.' << (int) date.getDay();
 }
 
diff --git a/src/openvic/Date.hpp b/src/openvic/Date.hpp
index 15b7219..61de9ba 100644
--- a/src/openvic/Date.hpp
+++ b/src/openvic/Date.hpp
@@ -33,7 +33,7 @@ namespace OpenVic {
 		explicit operator double() const;
 		explicit operator std::string() const;
 	};
-	std::ostream& operator<< (std::ostream& out, Timespan timespan);
+	std::ostream& operator<<(std::ostream& out, Timespan const& timespan);
 
 	// Represents an in-game date
 	// Note: Current implementation does not account for leap-years, or dates before Year 0
@@ -79,5 +79,5 @@ namespace OpenVic {
 		// Parsed from string of the form YYYY.MM.DD
 		static Date from_string(std::string const& date);
 	};
-	std::ostream& operator<< (std::ostream& out, Date date);
+	std::ostream& operator<<(std::ostream& out, Date const& date);
 }