Add getSdfAttrSafe function util that performs checks before reading sdf parameters. Not yet fully tested but putting it out there so i can continue later

Author: Aart Stuurman

cpprevolve/revolve/gazebo/util/SdfUtil.hpp

@@ -0,0 +1,42 @@
+#include <sdf/Element.hh>
+
+namespace revolve
+{
+    namespace gazebo
+    {
+
+        // Gets an attribute from an sdf element
+        // Throws std::runtime_error when not present.
+        // Can do types:
+        // - 'std::string'
+        // - 'bool'
+        // - 'double'
+        template <typename OfType>
+        OfType getSdfAttrSafe(sdf::ElementPtr sdf, std::string const &attribute)
+        {
+            static_assert(
+                std::is_same<OfType, std::string>::value ||
+                    std::is_same<OfType, double>::value ||
+                    std::is_same<OfType, bool>::value,
+                "Type not supported");
+            if (!sdf->HasAttribute(attribute) || !sdf->GetAttribute(attribute)->IsType<OfType>())
+            {
+                throw std::runtime_error(std::string("Could not get attribute: ") + attribute);
+            }
+            else
+            {
+                if constexpr (std::is_same<OfType, std::string>::value)
+                {
+                    return sdf->GetAttribute(attribute)->GetAsString();
+                }
+                else
+                {
+                    // Did not test this part yet
+                    OfType buffer;
+                    return sdf->GetAttribute(attribute)->Get<OfType>(buffer);
+                }
+            }
+        }
+
+    }
+}