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Alternative version of ros::param::param with return value #591

xperroni opened this Issue Mar 30, 2015 · 4 comments


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xperroni commented Mar 30, 2015

The template function ros::param::param sets a variable either to the value of a parameter, or if not available, a predefined default value. In cases where the variable is passed straight to a constructor or function call and then disregarded, more streamlined code could be written if the result value could be retrieved as a function return value, rather than through an output variable.

For example, the code below:

std::string path;
std::string format;
double fps;

param("~path", path, "video.mpg");
param("~format", format, "MPEG");
param("~fps", fps, 30.0);

VideoRecorder recorder(path, format, fps);

Could be more succinctly written as:

VideoRecorder recorder(
    param<std::string>("~path", "video.mpg"),
    param<std::string>("~format", "MPEG"),
    param<double>("~fps", 30.0)

If an alternative definition of ros::param::param such as this was available:

template<typename T>
T param(const std::string& param_name, const T& default_val)
  T param_val;
  param(param_name, param_val, default_val);
  return value;

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dirk-thomas commented Mar 30, 2015

Looks reasonable. Could you please provide a pull request adding this feature? It would be great if you would also include a unit test for it to ensure its working / continues to work in the future.

The existing function is implemented in two locations:

  • clients/roscpp/include/ros/param.h
  • clients/roscpp/include/ros/node_handle.h

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xperroni commented Mar 31, 2015

Done. I wasn't aware of the param method in NodeHandle or the unit test suite, thank you for the heads-up.


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xperroni commented Apr 7, 2015

Pull request sent and merged.

@xperroni xperroni closed this Apr 7, 2015


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tfoote commented Apr 7, 2015

For reference it was #592

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