fieldType QML Value Type

Represents the type of a field and related meta-data. More...

Properties

• capacity : uint64_t
• nestedTypeName : string
• stringCapacity : uint64_t
• typeId : uint8_t

Detailed Description

A constant for each type supported according to: http://design.ros2.org/articles/legacy_interface_definition.html and: http://design.ros2.org/articles/idl_interface_definition.html Order is loosely coupled to the order of appearance in the IDL 4.2 spec: https://www.omg.org/spec/IDL/4.2

Layout of constants across the 0-255 decimal values in the uint8:

- 000 : Reserved for "not set" - 001-048: Primitive types, strings, and reserved space for future primitive types - 049-096: Fixed sized array of primitive and string types - 097-144: Bounded Sequences of primitive and string types - 145-192: Unbounded Sequences of primitive and string types - 193-255: Reserved space for future array/sequence-like types

fieldType is a structured value type usable in QML. It maps directly to the type_description_interfaces::msg::FieldType ROS 2 message type.

Construct a fieldType in QML by assigning a JavaScript object whose keys are its component properties, or by setting those properties individually.

See also FieldTypePublisher and FieldTypeSubscriber.

Property Documentation

capacity : uint64_t

Only used when the type is an array or a bounded sequence.

In the case of an array, this is the fixed capacity of the array. In the case of a bounded sequence, this is the maximum capacity of the sequence. In all other cases this field is unused.

nestedTypeName : string

Only used when the type is a nested type or array/sequence of nested types.

This is limited to 255 characters. TODO(wjwwood): this 255 character limit was chosen due to this being the limit for DDSI-RTPS based middlewares, which is the most commonly used right now. We lack a ROS 2 specific limit in our design documents, but we should update this and/or link to the design doc when that is available.

stringCapacity : uint64_t

Only used when the type is a fixed or bounded string/wstring, or a array/sequence of those.

In the case of a fixed string/wstring, it is the fixed length of the string. In the case of a bounded string/wstring, it is the maximum capacity of the string. In the case of an array/sequence of fixed string/wstring, it is the fixed length of the strings. In the case of an array/sequence of bounded string/wstring, it is the maximum capacity of the strings. It is not currently possible to have different string capacities per element in the array/sequence.

typeId : uint8_t

Identifying number for the type of the field, using one of the above constants.