Update API to return const references to strings (#526)

Changes the following methods:
* CameraSensor::InfoTopic()
* Sensor::Name()
* Sensor::FrameId()
* Sensor::Parent()
* Sensor::Topic()

Signed-off-by: Steve Peters <[email protected]>

Author: scpeters

include/gz/sensors/CameraSensor.hh

@@ -122,7 +122,7 @@ namespace gz
 
       /// \brief Topic where camera info is published.
       /// \return Camera info topic.
-      public: std::string InfoTopic() const;
+      public: const std::string& InfoTopic() const;
 
       /// \brief Set baseline for stereo cameras. This is used to populate the
       /// projection matrix in the camera info message.

include/gz/sensors/Sensor.hh

@@ -147,19 +147,19 @@ namespace gz
 
       /// \brief Get name.
       /// \return Name of sensor.
-      public: std::string Name() const;
+      public: const std::string& Name() const;
 
       /// \brief FrameId.
       /// \return FrameId of sensor.
-      public: std::string FrameId() const;
+      public: const std::string& FrameId() const;
 
       /// \brief Set Frame ID of the sensor
       /// \param[in] _frameId Frame ID of the sensor
       public: void SetFrameId(const std::string &_frameId);
 
       /// \brief Get topic where sensor data is published.
       /// \return Topic sensor publishes data to
-      public: std::string Topic() const;
+      public: const std::string& Topic() const;
 
       /// \brief Set topic where sensor data is published.
       /// \param[in] _topic Topic sensor publishes data to.
@@ -176,7 +176,7 @@ namespace gz
 
       /// \brief Get parent link of the sensor.
       /// \return Parent link of sensor.
-      public: std::string Parent() const;
+      public: const std::string& Parent() const;
 
       /// \brief Get the sensor's ID.
       /// \return The sensor's ID.

src/CameraSensor.cc

@@ -592,7 +592,7 @@ rendering::CameraPtr CameraSensor::RenderingCamera() const
 }
 
 //////////////////////////////////////////////////
-std::string CameraSensor::InfoTopic() const
+const std::string& CameraSensor::InfoTopic() const
 {
   return this->dataPtr->infoTopic;
 }

src/Sensor.cc

@@ -282,13 +282,13 @@ SensorId Sensor::Id() const
 }
 
 //////////////////////////////////////////////////
-std::string Sensor::Name() const
+const std::string& Sensor::Name() const
 {
   return this->dataPtr->name;
 }
 
 //////////////////////////////////////////////////
-std::string Sensor::FrameId() const
+const std::string& Sensor::FrameId() const
 {
   return this->dataPtr->frameId;
 }
@@ -300,7 +300,7 @@ void Sensor::SetFrameId(const std::string &_frameId)
 }
 
 //////////////////////////////////////////////////
-std::string Sensor::Topic() const
+const std::string& Sensor::Topic() const
 {
   return this->dataPtr->topic;
 }
@@ -441,7 +441,7 @@ gz::math::Pose3d Sensor::Pose() const
 }
 
 //////////////////////////////////////////////////
-std::string Sensor::Parent() const
+const std::string& Sensor::Parent() const
 {
   return this->dataPtr->parent;
 }