Implemented changes as discussed on 2025-07-18 #1451
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Contributor
awillenbuecher-xq-tec
commented
Jul 18, 2025
- added Variant data type
- added Queue data type
- removed reflection from version 1.0
- removed restriction on equality of architecture
- made internal fields on ABI types private
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The created documentation from the pull request is available at: docu-html |
qor-lb
reviewed
Jul 18, 2025
docs/features/communication/abi_compatible_data_types/index.rst
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| It depends on some form of *type descriptions* being available to be able to interpret an unstructured sequence of bytes. | ||
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| Benefits of reflection include: | ||
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| * Consumers can perform additional consistency checks, because reflection provides a second, redundant description of the structure of the received data stream. | ||
| * Recorded data can be translated into a human-readable format (e.g., JSON or CSV) without having to know the type definitions beforehand; this allows general-purpose data recording and transformation tools. | ||
| * As a special case, if a data structure already contains *inline type descriptions* in the form of SOME/IP TLV tags, it doesn't need to be transformed before being sent over a SOME/IP connection. | ||
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| Inline Type Descriptions | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^ | ||
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| An explicit transformation step between the in-memory representation and the SOME/IP+TLV format can – in theory – be avoided by adding TLVs to ABI compatible types. | ||
| This approach, however, comes with significant downsides: | ||
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| * Adding inline type descriptions incurs a significant memory overhead across the board, and leads to worse cache behavior. | ||
| * It mandates TLV for *all* instances of *all* ABI compatible types, even when TLV is not needed (for example, in a non-TLV SOME/IP gateway). | ||
| * This might be mitigated by making TLV optional through a generic respectively a template parameter on the type declaration. | ||
| * SOME/IP's specification of big-endianness is in conflict with the requirement of native-endianness for ABI compatible types, making the feasibility of this approach questionable. | ||
| * SOME/IP doesn't support "unused" slots in dynamic arrays, so ABI compatible types containing *vectors* (which differentiate between the length and the capacity) couldn't be directly represented in SOME/IP anyway. | ||
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| Alternative Approach | ||
| ^^^^^^^^^^^^^^^^^^^^ | ||
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| Instead of inserting inline type descriptions into each instance of an ABI compatible type, the full type description can be made available to a consumer only once, either proactively or on request. | ||
| The consumer decides if it uses or ignores this metadata. |
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I would keep the alternative approach but move it to section "rejected ideas" below along with a description why we decided against it. This helps to avoid the same discussion twice.
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Done: Rejected Ideas
added 2 commits
July 18, 2025 17:05
- added Variant data type - added Queue data type - removed reflection from version 1.0 - removed restriction on equality of architecture - made internal fields on ABI types private
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