Limitations and Configuration

	Caution
	Recommended C++ Standards are C++17 and above. Library requires at least C++14! Pre C++14 compilers (C++11, C++03...) are not supported.

Boost.PFR library works with types that satisfy the requirements of SimpleAggregate: aggregate types without base classes, const fields, references, or C arrays:

struct simple_aggregate {  // SimpleAggregate
    std::string name;
    int age;
    boost::uuids::uuid uuid;
};

struct empty {             // SimpleAggregate
};

struct aggregate : empty { // not a SimpleAggregate
    std::string name;
    int age;
    boost::uuids::uuid uuid;
};

The library may work with aggregates that don't satisfy the requirements of SimpleAggregate, but the behavior tends to be non-portable.

Configuration Macro

By default Boost.PFR auto-detects your compiler abilities and automatically defines the configuration macro into appropriate values. If you wish to override that behavior, just define:

Table 26.2. Macros

Macro name	Effect
BOOST_PFR_USE_CPP17	Define to `1` if you wish to override Boost.PFR choice and use C++17 structured bindings for reflection. Define to `0` to override Boost.PFR choice and disable C++17 structured bindings usage.
BOOST_PFR_USE_LOOPHOLE	Define to `1` if you wish to override Boost.PFR choice and exploit CWG 2118 for reflection. Define to `0` to override Boost.PFR choice and disable CWG 2118 usage.
BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE	Define to `0` if you are hit by the template instantiation depth issues with `std::make_integer_sequence` and wish to use Boost.PFR version of that metafunction. Define to `1` to override Boost.PFR detection logic.
BOOST_PFR_HAS_GUARANTEED_COPY_ELISION	Define to `0` if your compiler does not implement C++17 guaranteed copy elision properly and fails to reflect aggregates with non-movable fields. Define to `1` to override Boost.PFR detection logic.

Details on Limitations

The Boost.PFRs reflection has some limitations that depend on a C++ Standard and compiler capabilities:

Static variables are ignored
T must be aggregate initializable without empty base classes
if T contains C arrays or it is inherited from non-empty type then the result of reflection may differ depending on the C++ version and library configuration
Additional limitations if BOOST_PFR_USE_CPP17 == 0:
- Non of the member fields should have a template constructor from one parameter.
- Additional limitations if BOOST_PFR_USE_LOOPHOLE == 0:
  - T must be constexpr aggregate initializable and all its fields must be constexpr default constructible
  - boost::pfr::get, boost::pfr::structure_to_tuple, boost::pfr::structure_tie, boost::pfr::tuple_element require T to be a POD type with built-in types only.

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