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// Copyright 2013-2017 Antony Polukhin
// Distributed under the Boost Software License, Version 1.0.
// (See the accompanying file LICENSE_1_0.txt
// or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
#include <boost/config.hpp>
template <class T>
void do_something(const T&) {}
#if !defined(BOOST_NO_CXX14_CONSTEXPR) && !defined(BOOST_NO_CXX11_CONSTEXPR)
// Implementation of this function is not essential for the example
template <std::size_t N>
constexpr bool starts_with(const char* name, const char (&ns)[N]) noexcept {
for (std::size_t i = 0; i < N - 1; ++i)
if (name[i] != ns[i])
return false;
return true;
}
//[type_index_constexpr14_namespace_example
/*`
The following example shows that `boost::typeindex::ctti_type_index` is usable at compile time on
a C++14 compatible compilers.
In this example we'll create and use a constexpr function that checks namespace of the provided type.
*/
#include <boost/type_index/ctti_type_index.hpp>
// Helper function that returns true if `name` starts with `substr`
template <std::size_t N>
constexpr bool starts_with(const char* name, const char (&substr)[N]) noexcept;
// Function that returns true if `T` declared in namespace `ns`
template <class T, std::size_t N>
constexpr bool in_namespace(const char (&ns)[N]) noexcept {
const char* name = boost::typeindex::ctti_type_index::type_id<T>().raw_name();
// Some compilers add `class ` or `struct ` before the namespace, so we need to skip those words first
if (starts_with(name, "class ")) {
name += sizeof("class ") - 1;
} else if (starts_with(name, "struct ")) {
name += sizeof("struct ") - 1;
}
return starts_with(name, ns) && starts_with(name + N - 1, "::");
}
/*`
Now when we have that wonderfull function, we can do static assertions and other compile-time validations:
*/
namespace my_project {
struct serializer {
template <class T>
void serialize(const T& value) {
static_assert(
in_namespace<T>("my_project::types") || in_namespace<T>("my_project::types_ext"),
"Only types from namespaces `my_project::types` and `my_project::types_ext` are allowed to be serialized using `my_project::serializer`"
);
// Actual implementation of the serialization goes below
// ...
do_something(value);
}
};
namespace types {
struct foo{};
struct bar{};
}
} // namespace my_project
int main() {
my_project::serializer s;
my_project::types::foo f;
my_project::types::bar b;
s.serialize(f);
s.serialize(b);
// short sh = 0;
// s.serialize(sh); // Fails the static_assert!
}
//] [/type_index_constexpr14_namespace_example]
#else // #if !defined(BOOST_NO_CXX14_CONSTEXPR) && !defined(BOOST_NO_CXX11_CONSTEXPR)
int main() {}
#endif
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