boost_describe.hpp

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// SPDX-FileCopyrightText: 2026 Jarosław Pelczar <jarek@jpelczar.com>
//
// SPDX-License-Identifier: BSD-2-Clause
 
#pragma once
 
#include "../microfmt.hpp"
#include <boost/describe.hpp>
#include <type_traits>
 
namespace microfmt {
 
namespace detail {
 
// Check if T has Boost.Describe members (only takes T)
template <typename T> using is_described_struct = boost::describe::has_describe_members<T>;
 
// Check if E is an enum registered with Boost.Describe
template <typename E>
struct is_described_enum
    : std::integral_constant<bool, std::is_enum_v<E> && boost::describe::has_describe_enumerators<E>::value> {};
 
} // namespace detail
 
// ============================================================================
// Formatter for Boost.Describe Reflected Enums
// ============================================================================
template <typename E> struct formatter<E, std::enable_if_t<detail::is_described_enum<E>::value>> {
  constexpr void parse(format_parse_context &ctx) noexcept { (void)ctx; }
 
  void format(E val, const sink &out) const noexcept {
    using Enumerators = boost::describe::describe_enumerators<E>;
    bool found = false;
 
    boost::mp11::mp_for_each<Enumerators>([&](auto D) noexcept {
      if (!found && D.value == val) {
        out.write(D.name);
        found = true;
      }
    });
 
    if (!found) {
      // Fallback: format raw underlying integer if value is unmapped/invalid
      using Underlying = std::underlying_type_t<E>;
      format_to(out, "static_cast<{}>({})",
                sizeof(Underlying) == 1   ? "uint8_t"
                : sizeof(Underlying) == 2 ? "uint16_t"
                                          : "uint32_t",
                static_cast<Underlying>(val));
    }
  }
};
 
// ============================================================================
// Formatter for Boost.Describe Reflected Structs & Classes
// ============================================================================
template <typename T> struct formatter<T, std::enable_if_t<detail::is_described_struct<T>::value>> {
  constexpr void parse(format_parse_context &ctx) noexcept { (void)ctx; }
 
  void format(const T &val, const sink &out) const noexcept {
    using Members = boost::describe::describe_members<T, boost::describe::mod_public>;
 
    out.put('{');
    bool first = true;
 
    boost::mp11::mp_for_each<Members>([&](auto D) noexcept {
      if (!first) {
        out.write(", ");
      }
      first = false;
 
      // Output member name
      out.write(D.name);
      out.write(": ");
 
      // Format member value recursively via microfmt
      format_to(out, "{}", val.*D.pointer);
    });
 
    out.put('}');
  }
};
 
} // namespace microfmt