The Basics

Overview

DataLayerGenerator is a header-only C++20 framework paired with a Python/Jinja2 code generator. You describe your application’s data model in JSON or YAML files and run the generator once (or as a CMake custom target) to produce a single datalayer.h header. The generated header uses only types from the src/include/ framework; the framework itself has no runtime dependencies beyond the C++20 standard library (fmt and pybind11 are optional).

Key properties:

Every datapoint is a constinit global — zero heap allocation.
Access control (READ_ONLY, WRITE_ONLY, READ_WRITE) is enforced at compile time via C++20 Concepts.
Range checking (Minimum / Maximum) is evaluated at the call site and returns a DataLayer::Detail::RangeCheck value — no exceptions.
Versioning metadata is embedded in groups and individual datapoints to support EEPROM upgrade paths.
Optional binary file persistence via Serialization / Deserialization (enabled with -DENABLE_FILE_PERSISTENCE=ON).
Optional fmt formatters for all generated structs and enums (enabled with -DENABLE_FMT=ON).
Optional Python bindings via pybind11 (enabled with -DENABLE_PYBIND11=ON).
Cross-compilation support for ARM Cortex-M4 (GCC ARM toolchain).

Architecture

Model files (JSON / YAML)
groups.json  datapoints.json  structs.json  enums.json  types.json
       │
       ▼
generator.py   ←  schema.json  +  Jinja2 templates
       │
  ┌────┴─────────────────────┐
  ▼                          ▼
generated/include/        generated/datalayer_example/
  datalayer.h               pythonBinding.cpp
  formatter.h
       │
       ▼
C++ application (embeds constinit datapoint objects)
  #include <include/datalayer.h>
  #include <include/formatter.h>

The src/include/ headers provide the type machinery:

helper.h
  ├── Version, FixedString, PersistenceType
  └── Helper::READ_ONLY / WRITE_ONLY / READ_WRITE tag types
      ├── detail.h
      │     └── BaseType<T>, RangeCheck, checkValue()
      ├── groupInfo.h
      │     └── DataLayer::GroupInfo<…>
      ├── datapoint.h
      │     └── DataLayer::DataPoint<T, Group, id, Access, …>
      ├── dataPointGroupMapping.h
      │     └── DataLayer::GroupDataPointMapping<GroupInfo, …Datapoints>
      ├── dispatcher.h
      │     └── DataLayer::Dispatcher<…GroupInfos>
      └── serialization.h  (guarded by USE_FILE_PERSISTENCE)
            └── Serialization<Data>, Deserialization<Data>

C++ Framework API

GroupInfo

template<uint16_t BaseId, FixedString Name, bool AllowUpgrade, PersistenceType persistence = PersistenceType::None, auto Version = Version{0, 0, 0}> struct GroupInfo

DataPoint

Warning

doxygenstruct: Cannot find class “DataLayer::DataPoint” in doxygen xml output for project “DataLayerGenerator” from directory: /home/runner/work/DataLayerGenerator/DataLayerGenerator/build-docs/doxygen/xml

GroupDataPointMapping

template<typename GroupInfo, typename ...Datapoints> struct GroupDataPointMapping

Dispatcher

template<typename ...GroupInfos> struct Dispatcher