enh(Nullable, Optional): reimplement using std::optional (#4502)

Foundation/include/Poco/Optional.h

@@ -20,7 +20,7 @@
 
 #include "Poco/Foundation.h"
 #include "Poco/Exception.h"
-#include <algorithm>
+#include <optional>
 
 
 namespace Poco {
@@ -53,40 +53,33 @@ class Optional
 	/// nillable == true.
 {
 public:
-	Optional():
+	Optional()
 		/// Creates an empty Optional.
-		_value(),
-		_isSpecified(false)
 	{
 	}
 
 	Optional(const C& value):
 		/// Creates a Optional with the given value.
-		_value(value),
-		_isSpecified(true)
+		_optional(value)
 	{
 	}
 
 	Optional(C&& value):
 		/// Creates a Optional by moving the given value.
-		_value(std::forward<C>(value)),
-		_isSpecified(true)
+		_optional(std::forward<C>(value))
 	{
 	}
 
 	Optional(const Optional& other):
 		/// Creates a Optional by copying another one.
-		_value(other._value),
-		_isSpecified(other._isSpecified)
+		_optional(other._optional)
 	{
 	}
 
 	Optional(Optional&& other) noexcept:
 		/// Creates a Optional by moving another one.
-		_value(std::move(other._value)),
-		_isSpecified(other._isSpecified)
+		_optional(std::move(other._optional))
 	{
-		other._isSpecified = false;
 	}
 
 	~Optional()
@@ -97,16 +90,14 @@ public:
 	Optional& assign(const C& value)
 		/// Assigns a value to the Optional.
 	{
-		_value = value;
-		_isSpecified = true;
+		_optional.emplace(value);
 		return *this;
 	}
 
 	Optional& assign(C&& value)
 		/// Moves a value into the Optional.
 	{
-		_value = std::move(value);
-		_isSpecified = true;
+		_optional.emplace(std::move(value));
 		return *this;
 	}
 
@@ -135,17 +126,14 @@ public:
 
 	Optional& operator = (Optional&& other) noexcept
 	{
-		_value = std::move(other._value);
-		_isSpecified = other._isSpecified;
-		other._isSpecified = false;
+		_optional = std::move(other._optional);
 		return *this;
 	}
 
 	void swap(Optional& other) noexcept
 	{
 		using std::swap;
-		swap(_value, other._value);
-		swap(_isSpecified, other._isSpecified);
+		swap(_optional, other._optional);
 	}
 
 	const C& value() const
@@ -153,10 +141,10 @@ public:
 		///
 		/// Throws a Poco::NullValueException if the value has not been specified.
 	{
-		if (_isSpecified)
-			return _value;
-		else
-			throw Poco::NullValueException();
+		if (_optional.has_value())
+			return _optional.value();
+
+		throw Poco::NullValueException();
 	}
 
 	const C& value(const C& deflt) const
@@ -164,24 +152,27 @@ public:
 		/// given default value if the Optional's
 		/// value has not been specified.
 	{
-		return _isSpecified ? _value : deflt;
+		if (_optional.has_value())
+			return _optional.value();
+
+		return deflt;
 	}
 
 	bool isSpecified() const
 		/// Returns true iff the Optional's value has been specified.
 	{
-		return _isSpecified;
+		return _optional.has_value();
 	}
 
 	void clear()
 		/// Clears the Optional.
 	{
-		_isSpecified = false;
+		_optional.reset();
 	}
 
 private:
-	C _value;
-	bool _isSpecified;
+
+	std::optional<C> _optional;
 };