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Value: Add a specialized rvalue reference of Get()

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The move `String(Value&&)` constructor tries to partially move `String`
values from a `Value` type. However, since there was no an appropriate
`Value::Get<T>()` implementation that binds to the requested move
operation, the compiler will actually not move the value but copy it
instead as the only available implementation of `Value::Get<T>()`
returns a const reference `const T&`. This commit adds a new overload
that returns a non-const reference and allows to optionally move the string
value of a Value type.
This commit is contained in:
Yonas Habteab 2025-02-27 17:38:05 +01:00
parent e308552ecc
commit 3e9292a349
5 changed files with 33 additions and 1 deletions
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2
lib/base/string.cpp
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@ -47,7 +47,7 @@ String::String(Value&& other)
String& String::operator=(Value&& other)
{
if (other.IsString())
m_Data = std::move(other.Get<String>());
*this = std::move(other.Get<String>()); // Will atomically bind to the move assignment operator below.
else
*this = static_cast<String>(other);

4
lib/base/value.cpp
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@ -9,9 +9,13 @@ using namespace icinga;
template class boost::variant<boost::blank, double, bool, String, Object::Ptr>;
template const double& Value::Get<double>() const;
template double& Value::Get<double>();
template const bool& Value::Get<bool>() const;
template bool& Value::Get<bool>();
template const String& Value::Get<String>() const;
template String& Value::Get<String>();
template const Object::Ptr& Value::Get<Object::Ptr>() const;
template Object::Ptr& Value::Get<Object::Ptr>();
const Value icinga::Empty;

10
lib/base/value.hpp
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@ -140,14 +140,24 @@ public:
return boost::get<T>(m_Value);
}
template<typename T>
T& Get()
{
return boost::get<T>(m_Value);
}
private:
boost::variant<boost::blank, double, bool, String, Object::Ptr> m_Value;
};
extern template const double& Value::Get<double>() const;
extern template double& Value::Get<double>();
extern template const bool& Value::Get<bool>() const;
extern template bool& Value::Get<bool>();
extern template const String& Value::Get<String>() const;
extern template String& Value::Get<String>();
extern template const Object::Ptr& Value::Get<Object::Ptr>() const;
extern template Object::Ptr& Value::Get<Object::Ptr>();
extern const Value Empty;

1
test/CMakeLists.txt
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@ -166,6 +166,7 @@ add_boost_test(base
base_string/index
base_string/find
base_string/vector_move
base_string/move_string_out_of_Value_type
base_timer/construct
base_timer/interval
base_timer/invoke

17
test/base-string.cpp
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@ -1,6 +1,7 @@
/* Icinga 2 | (c) 2012 Icinga GmbH | GPLv2+ */
#include "base/string.hpp"
#include "base/value.hpp"
#include <vector>
#include <BoostTestTargetConfig.h>
@ -126,4 +127,20 @@ BOOST_AUTO_TEST_CASE(vector_move)
BOOST_CHECK_EQUAL(oldAddr, newAddr);
}
// Test that the move constructor of icinga::String actually moves the underlying std::string out of a Value instance.
// The constructor overload is only available on non-Windows platforms though, so we need to skip the test on Windows.
BOOST_AUTO_TEST_CASE(move_string_out_of_Value_type)
{
#ifndef _MSC_VER
Value value("Icinga 2");
String other = value.Get<String>(); // We didn't request a move, so this should just copy the string.
BOOST_CHECK_EQUAL("Icinga 2", value.Get<String>());
BOOST_CHECK_EQUAL("Icinga 2", other);
String newStr = std::move(value);
BOOST_CHECK_EQUAL("", value.Get<String>());
BOOST_CHECK_EQUAL(newStr, "Icinga 2");
#endif /* _MSC_VER */
}
BOOST_AUTO_TEST_SUITE_END()