OARIS 3.0b2 FTF Avatar
  1. OMG Issue

OARIS3 — Consider the use of the IDL4 @optional annotation instead of unions

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  • Key: OARIS3-69
  • Status: open  
  • Source: Real-Time Innovations ( Dr. Gerardo Pardo-Castellote, Ph.D.)
  • Summary:

    The IDL4 language introduced the @optonal annotation that indicates that a structure member is optional. This is also supported by DDS-XTYPES. For example:

    // radians per second
typedef double azimuth_rate_type;
// radians per second
typedef double elevation_rate_type;
// meters per second
typedef double range_rate_type;

struct polar_velocity_type            {
    // The rate of change in azimuth corresponding to the velocity
    azimuth_rate_type azimuth_rate;
    // The rate of change in elevation corresponding to the velocity. 
    // Optional as some sensors provide no elevation information
    @optional elevation_rate_type elevation_rate;
    // The rate of change in range corresponding to the velocity. 
    // Optional as some sensors provide no range information
    // (e.g. most passive sensors)
    @optional range_rate_type range_rate;
};

    The OARIS IDL does not take advantage of this. Instead, it uses an older pre-IDL4 idiom using an extra "union" type. For example:

    // radians per second
typedef double azimuth_rate_type;
// radians per second
typedef double elevation_rate_type;
// meters per second
typedef double range_rate_type;

// a simple union type, to represent an optional value
union polar_velocity_elevation_rate_type switch (boolean)       {
    // the value when present
    case TRUE : elevation_rate_type value;
};

// a simple union type, to represent an optional value
union polar_velocity_range_rate_type switch (boolean)            {
    // the value when present
    case TRUE : range_rate_type value;
};

// Velocity defined in a polar reference frame as a described by a coordinate
// specification object
struct polar_velocity_type            {
    // The rate of change in azimuth corresponding to the velocity
    azimuth_rate_type azimuth_rate;
    // The rate of change in elevation corresponding to the velocity. 
    // Optional as some sensors provide no elevation information
    polar_velocity_elevation_rate_type elevation_rate;
    // The rate of change in range corresponding to the velocity. 
    // Optional as some sensors provide no range information
    // (e.g. most passive sensors)
    polar_velocity_range_rate_type range_rate;
};

    The extra union types result in more code generated to serialize and deserialize the data, increasing the size of the binary and decreasing performance.

    Moreover, the use of the @optional annotation allows for a more natural and optimized language mapping. For example, the recent IDL to C++ mapping maps optional members to the standard std::optional which is more natural for a C++ programmer.
  • Reported: OARIS 3.0a1 — Thu, 18 Jul 2024 03:58 GMT
  • Updated: Thu, 18 Jul 2024 03:58 GMT