6 files changed, 110 insertions, 5 deletions

diff --git a/src/crepe/util/CMakeLists.txt b/src/crepe/util/CMakeLists.txt
index 4be738a..94ed906 100644
--- a/src/crepe/util/CMakeLists.txt
+++ b/src/crepe/util/CMakeLists.txt
@@ -9,5 +9,7 @@ target_sources(crepe PUBLIC FILE_SET HEADERS FILES
 	Log.hpp
 	Proxy.h
 	Proxy.hpp
+	OptionalRef.h
+	OptionalRef.hpp
 )
 
diff --git a/src/crepe/util/Log.h b/src/crepe/util/Log.h
index d55b11e..fc0bb3a 100644
--- a/src/crepe/util/Log.h
+++ b/src/crepe/util/Log.h
@@ -34,11 +34,11 @@ class Log {
 public:
 	//! Log message severity
 	enum Level {
-		TRACE, //< Include (internal) function calls
-		DEBUG, //< Include dbg_logf output
-		INFO, //< General-purpose messages
-		WARNING, //< Non-fatal errors
-		ERROR, //< Fatal errors
+		TRACE, //!< Include (internal) function calls
+		DEBUG, //!< Include dbg_logf output
+		INFO, //!< General-purpose messages
+		WARNING, //!< Non-fatal errors
+		ERROR, //!< Fatal errors
 	};
 
 	/**
diff --git a/src/crepe/util/OptionalRef.h b/src/crepe/util/OptionalRef.h
new file mode 100644
index 0000000..3201667
--- /dev/null
+++ b/src/crepe/util/OptionalRef.h
@@ -0,0 +1,58 @@
+#pragma once
+
+namespace crepe {
+
+/**
+ * \brief Optional reference utility
+ *
+ * This class doesn't need to know the full definition of \c T to be used.
+ *
+ * \tparam T Value type
+ */
+template <typename T>
+class OptionalRef {
+public:
+	//! Initialize empty (nonexistant) reference
+	OptionalRef() = default;
+	//! Initialize reference with value
+	OptionalRef(T & ref);
+	/**
+	 * \brief Assign new reference
+	 *
+	 * \param ref Reference to assign
+	 *
+	 * \return Reference to this (required for operator)
+	 */
+	OptionalRef<T> & operator=(T & ref);
+	/**
+	 * \brief Retrieve this reference
+	 *
+	 * \returns Internal reference if it is set
+	 *
+	 * \throws std::runtime_error if this function is called while the reference it not set
+	 */
+	operator T &() const;
+	/**
+	 * \brief Check if this reference is not empty
+	 *
+	 * \returns `true` if reference is set, or `false` if it is not
+	 */
+	explicit operator bool() const noexcept;
+
+	/**
+	 * \brief Make this reference empty
+	 */
+	void clear() noexcept;
+
+private:
+	/**
+	 * \brief Reference to the value of type \c T
+	 *
+	 * \note This raw pointer is *not* managed, and only used as a reference!
+	 */
+	T * ref = nullptr;
+};
+
+} // namespace crepe
+
+#include "OptionalRef.hpp"
diff --git a/src/crepe/util/OptionalRef.hpp b/src/crepe/util/OptionalRef.hpp
new file mode 100644
index 0000000..4608c9e
--- /dev/null
+++ b/src/crepe/util/OptionalRef.hpp
@@ -0,0 +1,37 @@
+#pragma once
+
+#include <stdexcept>
+
+#include "OptionalRef.h"
+
+namespace crepe {
+
+template <typename T>
+OptionalRef<T>::OptionalRef(T & ref) {
+	this->ref = &ref;
+}
+
+template <typename T>
+OptionalRef<T>::operator T &() const {
+	if (this->ref == nullptr)
+		throw std::runtime_error("OptionalRef: attempt to dereference nullptr");
+	return *this->ref;
+}
+
+template <typename T>
+OptionalRef<T> & OptionalRef<T>::operator=(T & ref) {
+	this->ref = &ref;
+	return *this;
+}
+
+template <typename T>
+OptionalRef<T>::operator bool() const noexcept {
+	return this->ref != nullptr;
+}
+
+template <typename T>
+void OptionalRef<T>::clear() noexcept {
+	this->ref = nullptr;
+}
+
+} // namespace crepe
diff --git a/src/crepe/util/Proxy.h b/src/crepe/util/Proxy.h
index b34f7c6..789144a 100644
--- a/src/crepe/util/Proxy.h
+++ b/src/crepe/util/Proxy.h
@@ -16,6 +16,8 @@ template <typename T>
 class Proxy {
 public:
 	//! Set operator
+	Proxy & operator=(Proxy &);
+	//! Set operator
 	Proxy & operator=(const T &);
 	//! Get operator
 	operator const T &();
diff --git a/src/crepe/util/Proxy.hpp b/src/crepe/util/Proxy.hpp
index b9923db..ef2b69f 100644
--- a/src/crepe/util/Proxy.hpp
+++ b/src/crepe/util/Proxy.hpp
@@ -14,6 +14,12 @@ Proxy<T> & Proxy<T>::operator=(const T & val) {
 }
 
 template <typename T>
+Proxy<T> & Proxy<T>::operator=(Proxy & proxy) {
+	this->broker.set(T(proxy));
+	return *this;
+}
+
+template <typename T>
 Proxy<T>::operator const T &() {
 	return this->broker.get();
 }