core: Use std::optional to return an optional value

src/core/model/length.cc

@@ -32,7 +32,6 @@
 #include <ratio>
 #include <sstream>
 #include <string>
-#include <tuple>
 #include <type_traits>
 #include <unordered_map>
 #include <vector>
@@ -235,24 +234,19 @@ NS_LOG_COMPONENT_DEFINE ("Length");
 // Implement the attribute helper
 ATTRIBUTE_HELPER_CPP (Length);
 
-std::tuple<bool, Length>
+std::optional<Length>
 Length::TryParse (double value, const std::string& unitString)
 {
   NS_LOG_FUNCTION (value << unitString);
 
-  bool validUnit = false;
-  Length::Unit unit;
+  auto unit = FromString (unitString);
 
-  std::tie (validUnit, unit) = FromString (unitString);
-
-  Length length;
-
-  if (validUnit)
+  if (unit.has_value ())
     {
-      length = Length (value, unit);
+      return Length (value, *unit);
     }
 
-  return std::make_tuple (validUnit, length);
+  return std::nullopt;
 }
 
 Length::Length ()
@@ -276,19 +270,16 @@ Length::Length (double value, const std::string& unitString)
 {
   NS_LOG_FUNCTION (this << value << unitString);
 
-  bool validUnit;
-  Length::Unit unit;
+  auto unit = FromString (unitString);
 
-  std::tie (validUnit, unit) = FromString (unitString);
-
-  if (!validUnit)
+  if (!unit.has_value ())
     {
       NS_FATAL_ERROR ("A Length object could not be constructed from the unit "
                       "string '" << unitString << "', because the string is not associated "
                       "with a Length::Unit entry");
     }
 
-  m_value = Convert (value, unit, Length::Unit::Meter);
+  m_value = Convert (value, *unit, Length::Unit::Meter);
 }
 
 Length::Length (double value, Length::Unit unit)
@@ -577,7 +568,7 @@ ToName (Length::Unit unit, bool plural /*=false*/)
   return std::get<0> (iter->second);
 }
 
-std::tuple<bool, Length::Unit>
+std::optional<Length::Unit>
 FromString (std::string unitString)
 {
   using UnitTable = std::unordered_map<std::string, Length::Unit>;
@@ -654,16 +645,12 @@ FromString (std::string unitString)
 
   auto iter = UNITS.find (unitString);
 
-  bool valid = false;
-  Length::Unit unit;
-
   if (iter != UNITS.end ())
     {
-      valid = true;
-      unit = iter->second;
+      return iter->second;
     }
 
-  return std::make_tuple (valid, unit);
+  return std::nullopt;
 }
 
 std::ostream&

src/core/model/length.h

@@ -31,9 +31,9 @@
 
 #include <istream>
 #include <limits>
+#include <optional>
 #include <ostream>
 #include <string>
-#include <tuple>
 
 /**
  * \file
@@ -161,7 +161,7 @@ namespace ns3 {
  *   Addition is between two Length instances
  *
  * \code
- *   std::cout << Length(1, Length::Unit::Meter) + Length (2, Length::Unit::Meter);  
+ *   std::cout << Length(1, Length::Unit::Meter) + Length (2, Length::Unit::Meter);
  *   // output: "3 m"
  * \endcode
  *
@@ -170,7 +170,7 @@ namespace ns3 {
  *   Subtraction is between two Length instances
  *
  * \code
- *   std::cout << Length(3, Length::Unit::Meter) - Length (2, Length::Unit::Meter);  
+ *   std::cout << Length(3, Length::Unit::Meter) - Length (2, Length::Unit::Meter);
  *   // output: "1 m"
  * \endcode
  *
@@ -234,8 +234,8 @@ namespace ns3 {
  * \code
  *   Length m(5, Length::Unit::Meter);
  *
- *   std::cout << m << ", " 
- *             << m.As(Length::Unit::Kilometer) << ", " 
+ *   std::cout << m << ", "
+ *             << m.As(Length::Unit::Kilometer) << ", "
  *             << m.As(Length::Unit::Foot);
  *   //output: 5 m, 0.005 km, 16.4042 ft
  * \endcode
@@ -356,12 +356,11 @@ private:
    * \param value Numeric value of the new length
    * \param unit Unit that the value represents
    *
-   * \return A tuple containing the success or failure of the parsing and a Length
-   * object. If the boolean element is true, then the Length element contains the
-   * parsed result.  If the boolean element is false, the value of the Length
-   * element is undefined.
+   * \return A std::optional object containing the Length object constructed from
+   * the given value and unit, if the attempt to construct the Length object was
+   * successful.
    */
-  static std::tuple<bool, Length> TryParse (double value, const std::string& unit);
+  static std::optional<Length> TryParse (double value, const std::string& unit);
 
   /**
    * Default Constructor
@@ -667,12 +666,10 @@ std::string ToName (Length::Unit unit, bool plural = false);
  *
  * \param unitString String containing the symbol or name of a length unit
  *
- * \return A tuple containing a boolean and a Length::Unit.  When the boolean
- * is true, the Length::Unit contains a valid value. When the boolean is false,
- * a match for the string could not be found and the Length::Unit value is
- * undefined
+ * \return A std::optional object containing a Length::Unit if a match for the
+ * string could be found
  */
-std::tuple<bool, Length::Unit> FromString (std::string unitString);
+std::optional<Length::Unit> FromString (std::string unitString);
 
 /**
  * \ingroup length

src/core/test/length-test-suite.cc

@@ -39,7 +39,6 @@
 #include <map>
 #include <sstream>
 #include <string>
-#include <tuple>
 
 /**
  * \file
@@ -443,7 +442,7 @@ LengthTestCase::TestConstructLengthFromMeterString ()
 {
   const double value = 5;
 
-  TestConstructLengthFromString (value, value, 0, 
+  TestConstructLengthFromString (value, value, 0,
                                  {"m", "meter", "meters", "metre", "metres"});
 }
 
@@ -651,12 +650,9 @@ LengthTestCase::TestBuilderFreeFunctions ()
 void
 LengthTestCase::TestTryParseReturnsFalse ()
 {
-  bool result;
-  Length l;
+  auto l = Length::TryParse (1, "");
 
-  std::tie (result, l) = Length::TryParse (1, "");
-
-  AssertFalse (result, "TryParse returned true on bad input");
+  AssertFalse (l.has_value (), "TryParse returned true on bad input");
 }
 
 void
@@ -676,18 +672,15 @@ LengthTestCase::TestTryParseReturnsTrue ()
       TestInput input = entry.first;
       TestArgs args = entry.second;
 
-      bool result;
-      Length l;
+      auto l = Length::TryParse (input.first, input.second);
 
-      std::tie (result, l) = Length::TryParse (input.first, input.second);
-
-      AssertTrue (result, "TryParse returned false when expecting true");
+      AssertTrue (l.has_value (), "TryParse returned false when expecting true");
 
       std::stringstream stream;
       stream << "Parsing input (" << input.first << ", " << input.second
              << ") returned the wrong value";
 
-      NS_TEST_ASSERT_MSG_EQ_TOL (l.GetDouble (), args.first, args.second, stream.str ());
+      NS_TEST_ASSERT_MSG_EQ_TOL (l->GetDouble (), args.first, args.second, stream.str ());
     }
 
 }