Using IDL to define a data type

Supported IDL types
[https://fast-dds.docs.eprosima.com/en/latest/fastddsgen/dataTypes/dataTypes.html]

• Primitive types

• Arrays

• Sequences

• Maps

• Structures
  The following IDL structure:

  struct Structure
  {
      octet octet_value;
      long long_value;
      string string_value;
  };

Be converted to

class Structure
{
public:
    Structure();
    ~Structure();
    Structure(const Structure &x);
    Structure(Structure &&x);
    Structure& operator=(const Structure &x);
    Structure& operator=(Structure &&x);

    void octet_value(uint8_t _octet_value);
    uint8_t octet_value() const;
    uint8_t& octet_value();
    void long_value(int64_t _long_value);
    int64_t long_value() const;
    int64_t& long_value();
    void string_value(const std::string
        &_string_value);
    void string_value(std::string &&_string_value);
    const std::string& string_value() const;
    std::string& string_value();

private:
    uint8_t m_octet_value;
    int64_t m_long_value;
    std::string m_string_value;
};

Inherit from other structures

struct ParentStruct
{
    octet parent_member;
};

struct ChildStruct : ParentStruct
{
    long child_member;
};

//convert to 

class ParentStruct
{
    octet parent_member;
};

class ChildStruct : public ParentStruct
{
    long child_member;
};

• Unions

union Union switch(long)
{
   case 1:
    octet octet_value;
  case 2:
    long long_value;
  case 3:
    string string_value;
};
// convert to 
class Union
{
public:
    Union();
    ~Union();
    Union(const Union &x);
    Union(Union &&x);
    Union& operator=(const Union &x);
    Union& operator=(Union &&x);

    void d(int32_t __d);
    int32_t _d() const;
    int32_t& _d();

    void octet_value(uint8_t _octet_value);
    uint8_t octet_value() const;
    uint8_t& octet_value();
    void long_value(int64_t _long_value);
    int64_t long_value() const;
    int64_t& long_value();
    void string_value(const std::string
        &_string_value);
    void string_value(std:: string &&_string_value);
    const std::string& string_value() const;
    std::string& string_value();

private:
    int32_t m__d;
    uint8_t m_octet_value;
    int64_t m_long_value;
    std::string m_string_value;
};

• Bitsets
  Bitsets are a special kind of sturcture, which encloses a set of bits. A bitset can represent up to 64 bits. Each member is defined as bitfield and eases the access to a part of the bitset.
  Blow is a example named MyBitset, which store a total of 25 bits (3+10+12) and will require 32 bits in memory.
  (Which represents a rule that lowest primitive to store the bitset's size)
• The bitfield a allows us to access to the first 3 bits (0..2).
• The bitfield b allows us to access to the next 10 bits (3..12).
• The bitfield c allows us to access to the next 12 bits (13..24).

bitset MyBitset
{
    bitfield<3> a;
    bitfield<10> b;
    bitfield<12, int> c;
};
// resulting C++ code will be similar to 
class MyBitset
{
public:
    void a(char _a);
    char a() const;

    void b(uint16_t _b);
    uint16_t b() const;

    void c(int32_t _c);
    int32_t c() const;

private:
    std::bitset<25> m_bitset;
};

Internally, it is stored as a std::bitset. For each bitfield, get() and set() member functions are generated with the smaller possible primitive unsigned type to access it. In the case of bitfield ¡®c¡¯, the user has established that this accessing type will be int, so the generated code uses int32_t instead of automatically use uint16_t.
What is more, Bitsets can inherit from other bitsets, extending their member set.

bitset ParentBitset
{
  bitfield<3> parent_member;
};

bitset ChildBitset : ParentBitset
{
  bitfield<10> child_member;
};
// result converting is
class ParentBitset
{
    std::bitset<3> parent_member;
};

class ChildBitset : public ParentBitset
{
    std::bitset<10> child_member;
};

• Enumerations

enum Enumeration
{
    RED,
    GREEN,
    BLUE
};
// convert result is
enum Enumeration : uint32_t
{
    RED,
    GREEN,
    BLUE
};

• Bitmasks
  Bitmasks are a special kind of Enumeration to manage masks of bits, which allows defining bit masks based on their position.

@bit_bound(8)
bitmask MyBitMask
{
    @position(0) flag0,
    @position(1) flag1,
    @position(4) flag4,
    @position(6) flag6,
    flag7
};
// convert result is 
enum MyBitMask : uint8_t
{
    flag0 = 0x01 << 0,
    flag1 = 0x01 << 1,
    flag4 = 0x01 << 4,
    flag6 = 0x01 << 6,
    flag7 = 0x01 << 7
};

• Data types with a key
  In order to use keyed topics, the user should defind some key members inside the sturcture.
  Using @Key annotation before the members of the structure that are used as keys.
  These tags will be automatically detected by DDS-GEN. DDS-GEN will generates the serialization methods for they key generation function in TopicDataType(getKey(),this function will obtain the 128-bit MD5 digest of the big-dndian serialization of the Key Members).

struct MyType
{
    @Key long id;
    @Key string type;
    long positionX;
    long positionY;
};

Including other IDL files

Fast DDS-Gen uses a C/C++ preprocessor for this purpose, and #include directive can be used to include an IDL file.

#include "OtherFile.idl"
#include <AnotherFile.idl>

If Fast DDS-Gen does not find a C/C++ preprocessor in default system paths, the preprocessor path can be specified using parameter -ppPath. The parameter -ppDisable can be used to disable the usage of the C/C++ preprocessor.

Annotations

Allow users to define and use their own annotations as defined in the OMG in the OMG IDL 4.2 specification.
User annotations will be passed to TypeObject generated code if the -typeobject argument was used.

@annotation MyAnnotation
{
    long value;
    string name;
};

buildin annotations:
[https://fast-dds.docs.eprosima.com/en/latest/fastddsgen/dataTypes/dataTypes.html#annotations]

Forward Declaration

Fast DDS-Gen supports forward declarations. This allows declaring inter-dependant structures, unions, etc.

struct ForwardStruct;
union ForwardUnion;
struct ForwardStruct
{
    ForwardUnion fw_union;
};
union ForwardUnion switch (long)
{
    case 0:
        ForwardStruct fw_struct;
    default:
        string empty;
};

IDL 4.2 comments

• // [comments]
• /* [comments] */

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