mirror of https://github.com/oxen-io/oxen-mq
Browse Source
Add var::get/var::visit implementations of std::get/std::visit that get used if compiling for an old macos target, and use those. The issue is that on a <10.14 macos target Apple's libc++ is missing std::bad_variant_access, and so any method that can throw it (such as std::get and std::visit) can't be used. This workaround is ugly, but such is life when you want to support running on Apple platforms.pull/23/head
Jason Rhinelander
2 years ago
6 changed files with 120 additions and 31 deletions
@ -0,0 +1,87 @@
|
||||
#pragma once |
||||
// Workarounds for macos compatibility. On macOS we aren't allowed to touch anything in
|
||||
// std::variant that could throw if compiling with a target <10.14 because Apple fails hard at
|
||||
// properly updating their STL. Thus, if compiling in such a mode, we have to introduce
|
||||
// workarounds.
|
||||
//
|
||||
// This header defines a `var` namespace with `var::get` and `var::visit` implementations. On
|
||||
// everything except broken backwards macos, this is just an alias to `std`. On broken backwards
|
||||
// macos, we provide implementations that throw std::runtime_error in failure cases since the
|
||||
// std::bad_variant_access exception can't be touched.
|
||||
//
|
||||
// You also get a BROKEN_APPLE_VARIANT macro defined if targetting a problematic mac architecture.
|
||||
|
||||
#include <variant> |
||||
|
||||
#ifdef __APPLE__ |
||||
# include <AvailabilityVersions.h> |
||||
# if defined(__APPLE__) && MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_14 |
||||
# define BROKEN_APPLE_VARIANT |
||||
# endif |
||||
#endif |
||||
|
||||
#ifndef BROKEN_APPLE_VARIANT |
||||
|
||||
namespace var = std; // Oh look, actual C++17 support
|
||||
|
||||
#else |
||||
|
||||
// Oh look, apple.
|
||||
|
||||
namespace var { |
||||
|
||||
// Apple won't let us use std::visit or std::get if targetting some version of macos earlier than
|
||||
// 10.14 because Apple is awful about not updating their STL. So we have to provide our own, and
|
||||
// then call these without `std::` -- on crappy macos we'll come here, on everything else we'll ADL
|
||||
// to the std:: implementation.
|
||||
template <typename T, typename... Types> |
||||
constexpr T& get(std::variant<Types...>& var) { |
||||
if (auto* v = std::get_if<T>(&var)) return *v; |
||||
throw std::runtime_error{"Bad variant access -- variant does not contain the requested type"}; |
||||
} |
||||
template <typename T, typename... Types> |
||||
constexpr const T& get(const std::variant<Types...>& var) { |
||||
if (auto* v = std::get_if<T>(&var)) return *v; |
||||
throw std::runtime_error{"Bad variant access -- variant does not contain the requested type"}; |
||||
} |
||||
template <typename T, typename... Types> |
||||
constexpr const T&& get(const std::variant<Types...>&& var) { |
||||
if (auto* v = std::get_if<T>(&var)) return std::move(*v); |
||||
throw std::runtime_error{"Bad variant access -- variant does not contain the requested type"}; |
||||
} |
||||
template <typename T, typename... Types> |
||||
constexpr T&& get(std::variant<Types...>&& var) { |
||||
if (auto* v = std::get_if<T>(&var)) return std::move(*v); |
||||
throw std::runtime_error{"Bad variant access -- variant does not contain the requested type"}; |
||||
} |
||||
template <size_t I, typename Variant> |
||||
constexpr auto get(Variant&& var) { |
||||
return var::get<std::variant_alternative_t<I, std::remove_cv_t<std::remove_reference_t<Variant>>>>(std::forward<Variant>(var)); |
||||
} |
||||
|
||||
template <size_t I, size_t... More, class Visitor, class Variant> |
||||
constexpr auto visit_helper(Visitor&& vis, Variant&& var) { |
||||
if (var.index() == I) |
||||
return std::invoke(std::forward<Visitor>(vis), var::get<I>(std::forward<Variant>(var))); |
||||
else if constexpr (sizeof...(More) > 0) |
||||
return visit_helper<More...>(std::forward<Visitor>(vis), std::forward<Variant>(var)); |
||||
else |
||||
throw std::runtime_error{"Bad visit -- variant is valueless"}; |
||||
} |
||||
|
||||
template <size_t... Is, class Visitor, class Variant> |
||||
constexpr auto visit_helper(Visitor&& vis, Variant&& var, std::index_sequence<Is...>) { |
||||
return visit_helper<Is...>(std::forward<Visitor>(vis), std::forward<Variant>(var)); |
||||
} |
||||
|
||||
// Only handle a single variant here because multi-variant invocation is notably harder (and we
|
||||
// don't need it).
|
||||
template <class Visitor, class Variant> |
||||
constexpr auto visit(Visitor&& vis, Variant&& var) { |
||||
return visit_helper(std::forward<Visitor>(vis), std::forward<Variant>(var), |
||||
std::make_index_sequence<std::variant_size_v<std::remove_reference_t<Variant>>>{}); |
||||
} |
||||
|
||||
} // namespace var
|
||||
|
||||
#endif |
||||
Loading…
Reference in new issue