12.2. Supported Types

In order to provide maximum flexibility and capability to the defined dynamic types, eProsima Fast DDS supports several member types, ranging from simple primitives to nested structures.

This section describes the basic (not nested) supported types. For more complex structures and examples, please, refer to Complex Types.

12.2.1. Primitive Types

This section includes every simple kind:

BOOLEAN

INT64

BYTE

UINT16

CHAR8

UINT32

CHAR16

UINT64

INT16

FLOAT32

INT32

FLOAT64

FLOAT128

By definition, primitive types are self-described and can be created without configuration parameters. Therefore, DynamicTypeBuilderFactory exposes several functions to allow users create the dynamic type avoiding the DynamicTypeBuilder step. The DynamicTypeBuilder can still be used to create dynamic data of primitive types, as shown on the example below. The DynamicData class has a specific get() and set() functions for each primitive type of the list.

// Using Builders
DynamicTypeBuilder_ptr created_builder = DynamicTypeBuilderFactory::get_instance()->create_int32_builder();
DynamicType_ptr created_type = DynamicTypeBuilderFactory::get_instance()->create_type(created_builder.get());
DynamicData* data = DynamicDataFactory::get_instance()->create_data(created_type);
data->set_int32_value(1);

// Creating directly the Dynamic Type
DynamicType_ptr pType = DynamicTypeBuilderFactory::get_instance()->create_int32_type();
DynamicData* data2 = DynamicDataFactory::get_instance()->create_data(pType);
data2->set_int32_value(1);

12.2.2. String and WString

Strings are pretty similar to primitive types, the main difference being that they need to set the size of the buffer that they can manage. By default this size is set to 255 characters.

DynamicTypeBuilderFactory exposes the functions create_string_type() and create_wstring_type() to allow users create the DynamicTypes avoiding the DynamicTypeBuilder step. The DynamicTypeBuilder can still be used to create String type dynamic data, as shown on the example below.

// Using Builders
DynamicTypeBuilder_ptr created_builder = DynamicTypeBuilderFactory::get_instance()->create_string_builder(100);
DynamicType_ptr created_type = DynamicTypeBuilderFactory::get_instance()->create_type(created_builder.get());
DynamicData* data = DynamicDataFactory::get_instance()->create_data(created_type);
data->set_string_value("Dynamic String");

// Creating directly the Dynamic Type
DynamicType_ptr pType = DynamicTypeBuilderFactory::get_instance()->create_string_type(100);
DynamicData* data2 = DynamicDataFactory::get_instance()->create_data(pType);
data2->set_string_value("Dynamic String");

12.2.3. Alias

Alias types provide an alternative name to an already existing type. Once the DynamicData is created, users can access its information as if they were working with the base type.

DynamicTypeBuilderFactory exposes the function create_alias_type() to allow users create the Alias types avoiding the DynamicTypeBuilder step. The DynamicTypeBuilder can still be used to create Alias, as shown on the example below.

// Create the base type
DynamicTypeBuilder_ptr base_builder = DynamicTypeBuilderFactory::get_instance()->create_string_builder(100);
DynamicType_ptr base_type = DynamicTypeBuilderFactory::get_instance()->create_type(base_builder.get());

// Create alias using Builders
DynamicTypeBuilder_ptr builder = DynamicTypeBuilderFactory::get_instance()->create_alias_builder(base_type,
                "alias");
DynamicData* data = DynamicDataFactory::get_instance()->create_data(builder.get());
data->set_string_value("Dynamic Alias String");

// Create alias type directly
DynamicType_ptr pAliasType = DynamicTypeBuilderFactory::get_instance()->create_alias_type(base_type, "alias");
DynamicData* data2 = DynamicDataFactory::get_instance()->create_data(pAliasType);
data2->set_string_value("Dynamic Alias String");

12.2.4. Enumeration

An enumeration contains a set of supported values and a selected value among those supported. The supported values must be configured using the DynamicTypeBuilder, using the add_member() function for each supported value. The input to this function is the index and the name of the value we want to add.

The DynamicData class has functions get_enum_value() and set_enum_value() to work with value index or value name name strings.

// Add enumeration values using the DynamicTypeBuilder
DynamicTypeBuilder_ptr builder = DynamicTypeBuilderFactory::get_instance()->create_enum_builder();
builder->add_empty_member(0, "DEFAULT");
builder->add_empty_member(1, "FIRST");
builder->add_empty_member(2, "SECOND");

// Create the data instance
DynamicData* data = DynamicDataFactory::get_instance()->create_data(builder.get());

// Access value using the name
std::string sValue = "SECOND";
data->set_enum_value(sValue);
std::string sStoredValue;
data->get_enum_value(sStoredValue, MEMBER_ID_INVALID);

// Access value using the index
uint32_t uValue = 2;
data->set_enum_value(uValue);
uint32_t uStoredValue;
data->get_enum_value(uStoredValue, MEMBER_ID_INVALID);

12.2.5. Bitmask

Bitmasks are similar to enumeration types, but their members work as bit flags that can be individually turned on and off. Bit operations can be applied when testing or setting a bitmask value. DynamicData has the special functions get_bitmask_value() and set_bitmask_value() which allow to retrieve or modify the full value instead of accessing each bit.

Bitmasks can be bound to any number of bits up to 64.

uint32_t limit = 5; // Stores as "octet"

// Add bitmask flags using the DynamicTypeBuilder
DynamicTypeBuilder_ptr builder = DynamicTypeBuilderFactory::get_instance()->create_bitmask_builder(limit);
builder->add_empty_member(0, "FIRST");
builder->add_empty_member(1, "SECOND");

// Create the data instance
DynamicData_ptr data(DynamicDataFactory::get_instance()->create_data(builder.get()));

// Access the mask values using the name
data->set_bool_value(true, "FIRST");                // Set the "FIRST" bit
bool bSecondValue = data->get_bool_value("SECOND"); // Get the "SECOND" bit

// Access the mask values using the index
data->set_bool_value(true, 1);                      // Set the "SECOND" bit
bool bFirstValue = data->get_bool_value(0);         // Get the "FIRST" bit

// Get the complete bitmask as integer
uint64_t fullValue;
data->get_bitmask_value(fullValue);

12.2.6. Structure

Structures are the common complex types, they allow to add any kind of members inside them. They do not have any value, they are only used to contain other types.

To manage the types inside the structure, users can call the get() and set() functions according to the kind of the type inside the structure using their ids. If the structure contains a complex value, it should be used with loan_value to access to it and return_loaned_value to release that pointer. DynamicData manages the counter of loaned values and users can not loan a value that has been loaned previously without calling return_loaned_value before.

The ids must be consecutive starting by zero, and the DynamicType will change that Id if it doesn’t match with the next value. If two members have the same Id, after adding the second one, the previous will change its Id to the next value. To get the Id of a member by name, DynamicData exposes the function get_member_id_by_name().

// Build a structure with two fields ("first" as int32, "other" as uint64) using DynamicTypeBuilder
DynamicTypeBuilder_ptr builder = DynamicTypeBuilderFactory::get_instance()->create_struct_builder();
builder->add_member(0, "first", DynamicTypeBuilderFactory::get_instance()->create_int32_type());
builder->add_member(1, "other", DynamicTypeBuilderFactory::get_instance()->create_uint64_type());
DynamicType_ptr struct_type(builder->build());

// Create the data instance
DynamicData_ptr data(DynamicDataFactory::get_instance()->create_data(struct_type));

// Access struct members
data->set_int32_value(5, 0);
data->set_uint64_value(13, 1);

Structures allow inheritance, exactly with the same OOP meaning. To inherit from another structure, we must create the structure calling the create_child_struct_builder() of the factory. This function is shared with bitsets and will deduce our type depending on the parent’s type.

DynamicTypeBuilder_ptr child_builder =
        DynamicTypeBuilderFactory::get_instance()->create_child_struct_builder(builder.get());

12.2.7. Bitset

Bitset types are similar to structure types, but their members are merely bitfields, which are stored optimally. In the static version of bitsets, each bit uses just one bit in memory (with platform limitations) without alignment considerations. A bitfield can be anonymous (cannot be addressed) to skip unused bits within a bitset.

Each bitfield in a bitset can be modified through their minimal needed primitive representation.

Number of bits

Primitive

1

BOOLEAN

2-8

UINT8

9-16

UINT16

17-32

UINT32

33-64

UINT64

Each bitfield (or member) works like its primitive type with the only difference that the internal storage only modifies the involved bits instead of the full primitive value.

Bit_bound and position of the bitfield can be set using annotations (useful when converting between static and dynamic bitsets).

// Create bitfields with the appropriate type for their size
DynamicTypeBuilder_ptr base_type_byte_builder = DynamicTypeBuilderFactory::get_instance()->create_byte_builder();
auto base_type_byte = base_type_byte_builder->build();

DynamicTypeBuilder_ptr base_type_uint32_builder = DynamicTypeBuilderFactory::get_instance()->create_uint32_builder();
auto base_type_uint32 = base_type_uint32_builder->build();

// Create the bitset with two bitfields
DynamicTypeBuilder_ptr builder = DynamicTypeBuilderFactory::get_instance()->create_bitset_builder();
builder->add_member(0, "byte", base_type_byte);
builder->add_member(1, "uint32", base_type_uint32);

// Apply members' annotations
builder->apply_annotation_to_member(0, ANNOTATION_POSITION_ID, "value", "0");   // "byte" starts at position 0
builder->apply_annotation_to_member(0, ANNOTATION_BIT_BOUND_ID, "value", "2");  // "byte" is 2 bit length
builder->apply_annotation_to_member(1, ANNOTATION_POSITION_ID, "value", "10");  // "uint32" starts at position 10 (8 bits empty)
builder->apply_annotation_to_member(1, ANNOTATION_BIT_BOUND_ID, "value", "20"); // "uint32" is 20 bits length

// Create the data instance
DynamicData_ptr data(DynamicDataFactory::get_instance()->create_data(builder.get()));

// Access values
data->set_byte_value(234, 0);
data->set_uint32_value(2340, 1);
octet bValue;
uint32_t uValue;
data->get_byte_value(bValue, 0);
data->get_uint32_value(uValue, 1);

Bitsets allows inheritance, exactly with the same OOP meaning. To inherit from another bitset, we must create the bitset calling the create_child_struct_builder of the factory. This function is shared with structures and will deduce our type depending on the parent’s type.

DynamicTypeBuilder_ptr child_builder =
        DynamicTypeBuilderFactory::get_instance()->create_child_struct_builder(builder.get());

12.2.8. Union

Unions are a special kind of structures where only one of the members is active at the same time. To control these members, users must set the discriminator type that is going to be used to select the current member calling the create_union_builder function. The discriminator itself is a DynamicType of any primitive type, string type or union type.

Every member that is going to be added needs at least one union_case_index to set how it is going to be selected and, optionally, if it is the default value of the union.

// Create the union DynamicTypeBuilder with an int32 discriminator
DynamicType_ptr discriminator = DynamicTypeBuilderFactory::get_instance()->create_int32_type();
DynamicTypeBuilder_ptr builder = DynamicTypeBuilderFactory::get_instance()->create_union_builder(discriminator);

// Add the union members. "firts" will be the default value
builder->add_member(0, "first", DynamicTypeBuilderFactory::get_instance()->create_int32_type(), "", { 0 },
        true);
builder->add_member(0, "second", DynamicTypeBuilderFactory::get_instance()->create_int64_type(), "", { 1 },
        false);

// Create the data instance
DynamicType_ptr union_type = builder->build();
DynamicData_ptr data(DynamicDataFactory::get_instance()->create_data(union_type));

// Access the values using the member index
data->set_int32_value(9, 0);
data->set_int64_value(13, 1);

// Get the label of the currently selected member
uint64_t unionLabel;
data->get_union_label(unionLabel);

12.2.9. Sequence

A complex type that manages its members as a list of items allowing users to insert, remove or access to a member of the list. To create this type users need to specify the type that it is going to store and optionally the size limit of the list.

To ease the memory management of this type, DynamicData has these functions:

  • insert_sequence_data(): Creates a new element at the end of the list and returns the id of the new element.

  • remove_sequence_data(): Removes the element of the given index and refreshes the ids to keep the consistency of the list.

  • clear_data(): Removes all the elements of the list.

// Create a DynamicTypeBuilder for a sequence of two elements of type inte32
uint32_t length = 2;
DynamicType_ptr base_type = DynamicTypeBuilderFactory::get_instance()->create_int32_type();
DynamicTypeBuilder_ptr builder =
        DynamicTypeBuilderFactory::get_instance()->create_sequence_builder(base_type, length);

// Create the data instance
DynamicType_ptr sequence_type = builder->build();
DynamicData_ptr data(DynamicDataFactory::get_instance()->create_data(sequence_type));

// Insert and remove elements
MemberId newId, newId2;
data->insert_int32_value(10, newId);
data->insert_int32_value(12, newId2);
data->remove_sequence_data(newId);

12.2.10. Array

Arrays are pretty similar to sequences with two main differences: they can have multiple dimensions and they do not need their elements to be stored consecutively.

An array needs to know the number of dimensions it is managing. For that, users must provide a vector with as many elements as dimensions in the array. Each element in the vector represents the size of the given dimension. If the value of an element is set to zero, the default value applies (100).

Id values on the set() and get() functions of DynamicData correspond to the array index. To ease the management of array elements, every set() function in DynamicData class creates the item if the given index is empty.

To ease the memory management of this type, DynamicData has these functions:

  • insert_array_data(): Creates a new element at the end of the array and returns the id of the new element.

  • remove_array_data(): Clears the element of the given index.

  • clear_data(): Removes all the elements of the array.

  • get_array_index(): Returns the position id giving a vector of indexes on every dimension that the arrays support, which is useful in multidimensional arrays.

// Create an array DynamicTypeBuilder for a 2x2 elements of type int32
std::vector<uint32_t> lengths = { 2, 2 };
DynamicType_ptr base_type = DynamicTypeBuilderFactory::get_instance()->create_int32_type();
DynamicTypeBuilder_ptr builder =
        DynamicTypeBuilderFactory::get_instance()->create_array_builder(base_type, lengths);

// Create the data instance
DynamicType_ptr array_type = builder->build();
DynamicData_ptr data(DynamicDataFactory::get_instance()->create_data(array_type));

// Access elements in the multidimensional array
MemberId pos = data->get_array_index({1, 0});
data->set_int32_value(11, pos);
data->set_int32_value(27, pos + 1);
data->clear_array_data(pos);

12.2.11. Map

Maps contain a list of ‘key-value’ pair types, allowing users to insert, remove or modify the element types of the map. The main difference with sequences is that the map works with pairs of elements and creates copies of the key element to block the access to these elements.

To create a map, users must set the types of the key and the value elements, and, optionally, the size limit of the map.

To ease the memory management of this type, DynamicData has these functions:

  • insert_map_data(): Inserts a new key value pair and returns the ids of the newly created key and value elements.

  • remove_map_data(): Uses the given id to find the key element and removes the key and the value elements from the map.

  • clear_data(): Removes all the elements from the map.

// Create DynamicTypeBuilder for a map of two pairs of {key:int32, value:int32}
uint32_t length = 2;
DynamicType_ptr base = DynamicTypeBuilderFactory::get_instance()->create_int32_type();
DynamicTypeBuilder_ptr builder =
        DynamicTypeBuilderFactory::get_instance()->create_map_builder(base, base, length);

// Create the data instance
DynamicType_ptr map_type = builder->build();
DynamicData_ptr data(DynamicDataFactory::get_instance()->create_data(map_type));

// Add a new element to the map with key 1
DynamicData_ptr key(DynamicDataFactory::get_instance()->create_data(base));
MemberId keyId;
MemberId valueId;
key->set_int32_value(1);
data->insert_map_data(key.get(), keyId, valueId);

// Add a new element to the map with key 2
// insert_map_data creates a copy of the key, so the same instance can be reused
MemberId keyId2;
MemberId valueId2;
key->set_int32_value(2);
data->insert_map_data(key.get(), keyId2, valueId2);

// Set the value to the element with key 2, using the returned value Id
data->set_int32_value(53, valueId2);

// Remove elements from the map
data->remove_map_data(keyId);
data->remove_map_data(keyId2);