Where are useful message constructors, converters

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I'm relatively new to coding in/for ROS, and I'm looking at both the Python and the C++ side, but let's focus on C++ here.

There are all those useful classes (which are mappings of the ROS message types), like Pose, Twist, etc. But where are the related utility functions?

I mean, by what I've found so far, if I want to construct a Pose object, I have to:

geometry_msgs::Pose p;
p.position.x = MYXVAL;
p.position.x = MYYVAL;
p.position.x = MYZVAL;
p.orientation.x = ORXVAL;
p.orientation.y = ORYVAL;
p.orientation.z = ORZVAL;
p.orientation.w = ORWVAL;

Why can't I just do:

geometry_msgs::Pose p(geometry_msgs::Point(MYXVAL, MYYVAL, MYZVAL), geometry_msgs::Quaternion(ORXVAL, ORYVAL, ORZVAL, ORWVAL));

(which would of course be even shorter with the proper includes and using namespace declaration).

And where are my usual utility functions, like Vector3<->Quaternion or maybe Twist(Position+Facing)<->Pose(Position+Orientation)?

I could write the convenience constructors (which one would expect to be provided) myself, of course, but that's not the point of using a library like ROS/roscpp.