std::string s;
s.resize(33); // Avoid SSO
s = "😅";
std::cout << (const void*)s.data() << '\n';
auto s2 = std::move(s) + "🤣";
std::cout << (const void*)s2.data() << '\n';

std::move is not meaningless and allows for memory reuse.

However, changing operator+ to operato+= is fine by me.

not calculating the length of "."

Could ask for this explicitly with "."sv

Note that the result object is now copied from the concatenated string, because operator+= returns an lvalue, so the current change is possibly a pessimization.

Could fix this, and ask for NRVO by separating return statement:

(_Icu_version += '.') += _STD to_string(_Num_leap_seconds);
return _Icu_version;

But I doubt the value of optimizations here.

(_Icu_version += '.') += _STD to_string(_Num_leap_seconds);
return _Icu_version;

this is right.

Thanks! I pushed a commit to perform the concatenations on separate lines, since we conventionally don't perform multiple compound assignments on a single line.

Overall, I think this change is reasonable - taking advantage of the NRVO, and using the single-character overload instead of the one for arbitrary C strings. This code is not actually exercised in normal usage (it's bypassed unless the registry reports new leap seconds that we don't know about), so I don't think this is worth extreme micro-optimization, but I'm okay with the change here.

I manually tested this codepath since normal execution doesn't exercise it, and debugged into it to verify that the new code was getting picked up (i.e. verifying that I hadn't forgotten to set_environment.bat):

C:\GitHub\STL\out\x64>type meow.cpp

#include <chrono>
#include <print>
using namespace std;
using namespace std::chrono;

int main() {
    const tzdb& db = get_tzdb();
    println("Original version: {}", db.version);
    println(" Updated version: {}", _Tzdb_update_version(db.version, 1729));
}

C:\GitHub\STL\out\x64>cl /EHsc /nologo /W4 /std:c++latest /MTd /Od /Zi /Fdmeow.pdb meow.cpp && meow
meow.cpp
Original version: 2021a.27
 Updated version: 2021a.1729

We merge changes to our GitHub and MSVC-internal repos simultaneously, using a semi-manual "mirroring" process. To save time, we batch up PRs. Your PR will be part of the next batch! I'll post comments here as I prepare that merge.

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

Thanks for making the codebase more consistent about using the Named Return Value Optimization, and congratulations on your first microsoft/STL commit! 🎉 😻 🚀

This change is expected to ship in VS 2022 17.11 Preview 2.