This is done by simply not user-defining the copy constructor,
copy-assignment operator and destructor. See [1] for more info.
[1] http://accu.org/content/conf2014/Howard_Hinnant_Accu_2014.pdf
For the benchmark below (compiled with the next commit to allow sorting
SGPath instances), on Linux amd64 with g++ 6.3.0, I observe that
enabling SGPath move operations with this commit increases the
performance by 31% or 28% respectively, depending on whether I use this:
// Typical code that creates a data structure in several steps and
// benefits from move operations (the std::move() does nothing when
// running the test with move operations disabled: a copy is made).
auto p = SGPath::fromUtf8(randomString(0, 30));
v.emplace_back(std::move(p));
or that:
v.emplace_back(randomString(0, 30))
for the initialization code. Now the benchmark code:
using std::string;
static std::default_random_engine randomNumbersGenerator;
// Utility function: generate a random string whose length is in the
// [minLen, maxLen] range.
string randomString(string::size_type minLen, string::size_type maxLen)
{
std::uniform_int_distribution<string::size_type> sLenDist(minLen, maxLen);
std::uniform_int_distribution<int> byteDist(0, 255);
auto randomByte = std::bind(byteDist, randomNumbersGenerator);
string::size_type len = sLenDist(randomNumbersGenerator);
string str;
while (str.size() < len) {
str += std::char_traits<char>::to_char_type(randomByte());
}
return str;
}
// The test function, run with nbIterations = 500000, minSize = 0 and
// maxSize = 200 to obtain the figures given above.
void SGPath_perfTest(std::size_t nbIterations,
std::size_t minSize, std::size_t maxSize)
{
std::uniform_int_distribution<std::size_t> sizeDist(minSize, maxSize);
auto randomSize = std::bind(sizeDist, randomNumbersGenerator);
std::chrono::time_point<std::chrono::system_clock> start, end;
start = std::chrono::system_clock::now();
vector<SGPath> v;
for (std::size_t i=0; i < nbIterations; i++) {
v = vector<SGPath>{}; // start anew
for (std::size_t j=0; j < randomSize(); j++) {
v.emplace_back(randomString(0, 30));
}
std::shuffle(v.begin(), v.end(), randomNumbersGenerator);
std::sort(v.begin(), v.end());
}
end = std::chrono::system_clock::now();
std::chrono::duration<double> elapsedSecs = end - start;
std::cout << elapsedSecs.count() << "\n"; // duration in seconds
}
Florent Rougon
1310092c0c