format_arg.h

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#pragma once
 
#include "di/container/string/string_view_impl.h"
#include "di/format/concepts/format_context.h"
#include "di/format/concepts/formattable.h"
#include "di/function/monad/monad_try.h"
#include "di/util/voidify.h"
#include "di/vocab/variant/prelude.h"
 
namespace di::fmt {
template<concepts::Formattable... Types>
using ConstexprFormatArg = Variant<Types&..., Void>;
 
template<concepts::FormatContext Context>
class ErasedArg {
private:
    using Encoding = meta::Encoding<Context>;
 
    template<concepts::Formattable T>
    constexpr static auto erased_format(void* value, FormatParseContext<Encoding>& parse_context, Context& context,
                                        bool debug) -> di::Result<void> {
        auto formatter = DI_TRY(fmt::formatter<T, Encoding>(parse_context, debug));
        return formatter(context, *static_cast<meta::RemoveCVRef<T>*>(value));
    }
 
public:
    template<concepts::Formattable T>
    constexpr explicit ErasedArg(T&& value)
        : m_pointer(util::voidify(util::addressof(value))), m_do_format(erased_format<T>) {}
 
    constexpr auto do_format(FormatParseContext<Encoding>& parse_context, Context& context, bool debug)
        -> Result<void> {
        return m_do_format(m_pointer, parse_context, context, debug);
    }
 
private:
    void* m_pointer;
    Result<void> (*m_do_format)(void*, FormatParseContext<Encoding>&, Context&, bool debug);
};
 
template<concepts::FormatContext Context>
using FormatArg = Variant<Void, bool, meta::EncodingCodePoint<meta::Encoding<Context>>, int, unsigned int,
                          long long int, unsigned long long int, /* float, double, long double, */
                          container::string::StringViewImpl<meta::Encoding<Context>>, void const*, ErasedArg<Context>>;
}