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construct/include/ircd/util/va_rtti.h

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2018-02-04 03:22:01 +01:00
// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
2018-02-04 03:22:01 +01:00
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.
#pragma once
#define HAVE_IRCD_UTIL_VA_RTTI_H
namespace ircd {
inline namespace util
{
struct va_rtti;
const size_t VA_RTTI_MAX_SIZE
{
12
};
}}
//
// Similar to a va_list, but conveying std-c++ type data acquired from a variadic template
// parameter pack acting as the ...) elipsis. This is used to implement fmt::snprintf(),
// exceptions and logger et al in their respective translation units rather than the header
// files.
//
// Limitations: The choice of a fixed array of N is because std::initializer_list doesn't
// work here and other containers may be heavy in this context. Ideas to improve this are
// welcome.
//
struct ircd::util::va_rtti
:std::array<std::tuple<const void *, const std::type_info *>, ircd::util::VA_RTTI_MAX_SIZE>
{
using base_type = std::array<value_type, ircd::util::VA_RTTI_MAX_SIZE>;
static constexpr size_t max_size()
{
return std::tuple_size<base_type>();
}
size_t argc;
const size_t &size() const
{
return argc;
}
template<class... Args>
va_rtti(Args&&... args)
:base_type
{{
std::make_tuple(std::addressof(args), std::addressof(typeid(Args)))...
}}
,argc
{
sizeof...(args)
}
{
assert(argc <= max_size());
static_assert
(
sizeof...(args) <= max_size(),
"Too many arguments to va_rtti"
);
}
};
static_assert
(
sizeof(ircd::util::va_rtti) == (ircd::util::va_rtti::max_size() * 16) + 8,
"va_rtti should be (8 + 8) * N + 8;"
" where 8 + 8 are the two pointers carrying the argument and its type data;"
" where N is the max arguments;"
" where the final + 8 bytes holds the actual number of arguments passed;"
);