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find_optional.cmake
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find_optional.cmake
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# SPDX-License-Identifier: GPL-3.0-or-later
# SPDX-FileCopyrightText: 2018 Rolf Eike Beer <eike@sf-mail.de>.
# find out if std::optional can be used
set(OPT_TESTCODE
"
#ifdef CXX17_OPTIONAL
#include <optional>
#elif defined(CXX14_EXP_OPTIONAL)
#include <experimental/optional>
namespace std {
using experimental::optional;
}
#endif
int main(void)
{
std::optional<int> x = 1;
return x ? *x - 1 : 1;
}
"
)
if (CMAKE_CXX_STANDARD LESS 17)
set(OLD_STANDARD "${CMAKE_CXX_STANDARD}")
set(CMAKE_CXX_STANDARD 17)
endif ()
check_cxx_source_compiles("${OPT_TESTCODE}" CXX17_OPTIONAL)
if (OLD_STANDARD)
if (NOT CXX17_OPTIONAL)
set(CMAKE_CXX_STANDARD ${OLD_STANDARD})
endif ()
unset(OLD_STANDARD)
endif ()
if (NOT CXX17_OPTIONAL)
if (CMAKE_CXX_STANDARD LESS 14)
set(OLD_STANDARD "${CMAKE_CXX_STANDARD}")
set(CMAKE_CXX_STANDARD 14)
endif ()
check_cxx_source_compiles("${OPT_TESTCODE}" CXX14_EXP_OPTIONAL)
if (NOT CXX14_EXP_OPTIONAL)
set(CMAKE_CXX_STANDARD ${OLD_STANDARD})
endif ()
unset(OLD_STANDARD)
configure_file("${CMAKE_CURRENT_SOURCE_DIR}/optional.hxx.in"
"${CMAKE_CURRENT_BINARY_DIR}/optional"
@ONLY)
endif ()
unset(OPT_TESTCODE)