vector push_back vs emplace_back

[dull spindle]

I already know that in push_back a temporary is created and copied after the last element of the vector and in emplace_back object is constructed in place by forwarding arguments.

But with emplace_back objects can also be passed which in turn copy constructs at the end of vector.

So what can be other use case of push_back which cannot be achieved by emplace_back ?

[lost mulch]

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[lucid notch]

push_back is all-around simpler by virtue of not being a template, if you're uncomfortable with working with templates and reading the diagnostic errors it's just easier to use

[compact copper]

https://quuxplusone.github.io/blog/2021/03/03/push-back-emplace-back/

I personally use push_back when copying or moving, and emplace_back when forwarding args

[fathom torrent]

Given a std::vector<std::vector<int>> v; you can do v.push_back({1, 2, 3, 4, 5});. The emplace_back versions are more complicated because it lacks the type deduction.

[dull spindle]

Then how would we achieve your above example with emplace_back

[fathom torrent]

v.emplace_back(std::vector<int>{1, 2, 3, 4, 5}); 🤷

Actually anything with brace initialization sucks for emplace_back because it doesn't use brace initialization.

struct Point {
  int x;
  int y;
};

std::vector<Point> points;
points.push_back({1, 2}); //neat
points.emplace_back(Point{1, 2}); //less neat

[dull spindle]

As expected. Also If I am not wrong the temporary materialised object is moved, right ?

[fathom torrent]

They both move.

Unnecessarily

But what can you do. It's not like the nanosecond matters.

[dull spindle]

I usually use emplace_back when I don't need a copy or more at all.
As per my understanding, normal tasks doesn't matter much if temporary is moved or copied, expect working in like embedded or mobile environment

[lost mulch]

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