C++23 std::formatter implementations for WinRT classes

winrt_formatters.h

#ifndef WINRT_FORMATTERS_H
#define WINRT_FORMATTERS_H

#include <windows.h>

#include <winrt/base.h>

#include <string>
#include <format>

template<>
struct std::formatter<std::wstring> : std::formatter<std::string> {
    auto format(const std::wstring& s, std::format_context& ctx) const {
        auto inputLength = static_cast<int>(s.size());
        auto size = WideCharToMultiByte(CP_UTF8, 0, s.data(), inputLength, nullptr, 0, nullptr, nullptr) + 1;
        std::string result(size, 0);
        WideCharToMultiByte(CP_UTF8, 0, s.data(), inputLength, result.data(), size, nullptr, nullptr);
        result.resize(size - 1);
        return std::formatter<std::string>::format(result, ctx);
    }
};

template<>
struct std::formatter<winrt::hstring> : std::formatter<std::string> {
    auto format(const winrt::hstring& s, std::format_context& ctx) const {
        auto inputLength = static_cast<int>(s.size());
        auto size = WideCharToMultiByte(CP_UTF8, 0, s.data(), inputLength, nullptr, 0, nullptr, nullptr) + 1;
        std::string result(size, 0);
        WideCharToMultiByte(CP_UTF8, 0, s.data(), inputLength, result.data(), size, nullptr, nullptr);
        result.resize(size - 1);
        return std::formatter<std::string>::format(result, ctx);
    }
};

template<>
struct std::formatter<winrt::hresult> : std::formatter<uint32_t> {
    auto format(winrt::hresult result, std::format_context& ctx) const {
        return std::format_to(ctx.out(), "0x{:08X}", result.value);
    }
};

#endif // WINRT_FORMATTERS_H