roscpp missing getParam() for lists and dictionaries

[b-adkins]

"roscpp's parameter API supports all of [ROS Parameter Server's data types], though it is only easy to use strings, integers, floats and booleans." (roscpp Parameter Server)

Why? I don't see why an application developer needs to learn XmlRpc and re-implement the wheel. I believe it's quite doable to reconstruct lists and dictionaries (at least of primitives) entered in YAML to the parameter server.

I propose a patch with templated varieties of NodeHandle::getParam() and param::get() that:

Extracts lists as

// C++ STL style:
std::vector<type> the_list_cpp;

// Possibly C style:
type* the_list_c;

Extracts dictionaries as

// C++ STL style:
std::map<std::string, type> the_dictionary;

// C style:
char* keys[];
type* values;

Proposed interface:
(n_max is the maximum elements the passed buffer(s) can hold, to prevent buffer overrun)

// C++ STL style:
template<typename T> bool getParam(const std:string& key, std::vector<T>& l) const;
template<typename T> bool getParam(const std:string& key, std::map<std::string, T>& d) const;

// C style:
template<typename T> bool getParam(const std:string& key, T* l, int n_max) const;
template<typename T> bool getParam(const std:string& key, char* s[], T* v, int n_max) const;

The C++-style versions would be very easy to use. The C-style types may be useful for performance.

I've essentially already written these for another project. I would like to offer my code as part of this proposed patch.

EDIT: For easy reference, here is <ros/param.h>:
https://github.com/ros/ros_comm/blob/groovy-devel/clients/roscpp/include/ros/param.h

Also note that the methods would need to be wrapped NodeHandle:
https://github.com/ros/ros_comm/blob/groovy-devel/clients/roscpp/src/libros/node_handle.cpp

[jbohren]

I think many of us have implemented similar things. It would be great to see some of them added to the core libraries.
See my vector param implementation here: https://github.com/jhu-lcsr/terse_roscpp/blob/master/include/terse_roscpp/param.h

Do you have an implementation of your own floating around somewhere?

[b-adkins]

Sorry for the delayed response. I have getters for vectors and maps
which use the same conventions as the ros code. I'll post them when I
figure out how to use GitHub.

Bea

On 8/21/2013 8:54 AM, Jonathan Bohren wrote:

I think many of us have implemented similar things. It would be great
to see some of them added to the core libraries.
See my vector param implementation here:
https://github.com/jhu-lcsr/terse_roscpp/blob/master/include/terse_roscpp/param.h

Do you have an implementation of your own floating around somewhere?

—
Reply to this email directly or view it on GitHub
#263 (comment).

[b-adkins]

Here is my code.
https://gist.github.com/b-adkins/6362327

Some thoughts:

• I made the style copy-pasteable right into <ros/param.h>.
• The templates can fill a vector or a map with a single type of value, thus the underlying param server value must convertible to that type.
• On the variable names, I chose "d" for dictionary and "l" for list (as they are called in YAML).
• By creating an isType(testee) method, it has shorter and less repetitive template specialization.

[jbohren]

@b-adkins The best way to contribute a patch is by "forking" a given repository, making your changes in the fork, and then creating a "pull request" (tutorial here). I've been waiting for three years or so for someone to implement these features, and I think part of it is because while most submissions work, they're not up to the standards of the ROS dev team. I took some time thisafternoon to create a patch with a similar scope, but a little more polished: #279 and hopefully this can get merged in soon and roscpp can stop envying rospy...

[dirk-thomas]

PR has been merged and package released.