From 1deafa3ad1644cee66602b4bb5499e0de8f4480a Mon Sep 17 00:00:00 2001
From: Kelvin Sherlock <ksherlock@gmail.com>
Date: Sun, 8 Jan 2017 20:17:10 -0500
Subject: [PATCH] add c++17 optional

---
 Makefile       |   2 +-
 expression.cpp |   8 ++-
 expression.h   |   4 +-
 optional.h     | 139 +++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 146 insertions(+), 7 deletions(-)
 create mode 100644 optional.h

diff --git a/Makefile b/Makefile
index 937a589..ec82e73 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 LINK.o = $(LINK.cc)
-CXXFLAGS = -std=c++11 -g -Wall
+CXXFLAGS = -std=c++14 -g -Wall
 CCFLAGS = -g
 
 DUMP_OBJS = dumpobj.o disassembler.o zrdz_disassembler.o
diff --git a/expression.cpp b/expression.cpp
index abb1c58..801ae4f 100644
--- a/expression.cpp
+++ b/expression.cpp
@@ -145,9 +145,7 @@ bool simplify_expression(expression &e) {
  * if force is true, treat OP_LOC records as OP_VAL (for omf)
  */
 
-// should return std::optional<uint32_t>...
-
-uint32_t evaluate_expression(expression &e, bool force) {
+optional<uint32_t> evaluate_expression(expression &e, bool force) {
 	std::vector<expr> tmp;
 	for (const auto &t : e.stack) {
 		if (t.tag == OP_LOC && force) {
@@ -163,7 +161,7 @@ uint32_t evaluate_expression(expression &e, bool force) {
 		}
 	}
 
-	if (tmp.size() == 1 && tmp.front().tag == OP_VAL) return tmp.front().value;
-	return 0;
+	if (tmp.size() == 1 && tmp.front().tag == OP_VAL) return optional<uint32_t>(tmp.front().value);
+	return optional<uint32_t>();
 }
 
diff --git a/expression.h b/expression.h
index db3c56d..0047681 100644
--- a/expression.h
+++ b/expression.h
@@ -4,6 +4,8 @@
 #include <stdint.h>
 #include <vector>
 
+#include "optional.h"
+
 struct expr {
 	expr(int t = 0, uint32_t v = 0, uint32_t s = 0)
 		: tag(t), value(v), section(s)
@@ -25,7 +27,7 @@ struct expression {
 
 };
 
-uint32_t evaluate_expression(expression &e, bool force = false);
+optional<uint32_t> evaluate_expression(expression &e, bool force = false);
 
 bool simplify_expression(expression &e);
 
diff --git a/optional.h b/optional.h
new file mode 100644
index 0000000..b38ca32
--- /dev/null
+++ b/optional.h
@@ -0,0 +1,139 @@
+#ifndef __optional_h__
+#define __optional_h__
+
+#include <type_traits>
+#include <stdexcept>
+
+class bad_optional_access : public std::exception {
+public:
+	virtual const char* what() const noexcept {
+		return "bad optional access";
+	}
+};
+
+template<class T>
+class optional {
+public:
+	typedef T value_type;	
+
+	optional() = default;
+
+	optional( const optional& other ) {
+		if (other._engaged) {
+			new (std::addressof(_data)) T(*other);
+			_engaged = true;
+		}
+	}
+
+	optional( const optional&& other ) {
+		if (other._engaged) {
+			new (std::addressof(_data)) T(std::move(*other));
+			_engaged = true;
+		}
+	}
+
+	template < class U >
+	optional( const optional<U>& other ) {
+		if (other._engaged) {
+			new (std::addressof(_data)) T(*other);
+			_engaged = true;
+		}
+	}
+
+	template < class U >
+	optional( optional<U>&& other ) {
+		if (other._engaged) {
+			new (std::addressof(_data)) T(std::move(*other));
+			_engaged = true;
+		}
+	}
+
+
+	template<class U = T>
+	optional(U &&value) {
+		new(std::addressof(_data)) T(std::forward<U>(value));
+		_engaged = true;
+	}
+
+
+
+	~optional() {
+		reset();
+	}
+
+
+	constexpr explicit operator bool() const {
+		return _engaged;
+	}
+
+	constexpr bool has_value() const {
+		return _engaged;
+	}
+
+	/* these should throw ... */
+	constexpr T& value() & {
+		if (!_engaged) throw bad_optional_access();
+		return *reinterpret_cast<T*>(std::addressof(_data));
+	}
+
+	constexpr const T & value() const & {
+		if (!_engaged) throw bad_optional_access();
+		return *reinterpret_cast<const T*>(std::addressof(_data));
+	}
+
+	constexpr T&& value() && {
+		if (!_engaged) throw bad_optional_access();
+		return *reinterpret_cast<T*>(std::addressof(_data));
+	}
+
+	constexpr const T&& value() const && {
+		if (!_engaged) throw bad_optional_access();
+		return *reinterpret_cast<const T*>(std::addressof(_data));
+	}
+
+
+	template< class U > 
+	constexpr T value_or( U&& default_value ) const& {
+		return bool(*this) ? **this : static_cast<T>(std::forward<U>(default_value));
+	}
+
+	template< class U > 
+	constexpr T value_or( U&& default_value ) && {
+		return bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(default_value));
+	}
+
+	constexpr const T* operator->() const {
+		return reinterpret_cast<const T*>(std::addressof(_data));
+	}
+	constexpr T* operator->() {
+		return reinterpret_cast<T*>(std::addressof(_data));
+	}
+
+	constexpr const T& operator*() const& {
+		return *reinterpret_cast<const T*>(std::addressof(_data));
+	}
+	constexpr T& operator*() & {
+		return *reinterpret_cast<T*>(std::addressof(_data));
+	}
+	constexpr const T&& operator*() const&& {
+		return *reinterpret_cast<const T*>(std::addressof(_data));
+	}
+	constexpr T&& operator*() && {
+		return *reinterpret_cast<T*>(std::addressof(_data));
+	}
+
+
+	void reset() {
+		if (_engaged) {
+			reinterpret_cast<const T*>(std::addressof(_data))->~T();
+			_engaged = false;
+		}
+	}
+
+private:
+	bool _engaged = false;
+	typename std::aligned_storage<sizeof(T), alignof(T)>::type _data;
+};
+
+#endif
+