CODEWITHSUNDEEP
c++performancecontainersstdmapstd
Gordem
Gordem

Reputation: 115

Inserting heavy objects into std::map

How many times exactly copies the VeryHeavy(args...) in this code?

map.emplace(std::pair<VeryHeavyKey, VeryHeavy>(key, VeryHeavy(args...)));

Or, maybe, there is better to use std::make_pair? Are there any standartized warranties on copying objects? What's the right way to insert heavy objects into std::map without copying?

Upvotes: 2

Views: 105

Answers (1)

Caleth
Caleth

Reputation: 62636

What's the right way to insert heavy object into std::map without copying?

prior to C++17

map.emplace(std::piecewise_construct,
              std::forward_as_tuple(std::move(key)),
              std::forward_as_tuple(args...));

post C++17

map.try_emplace(std::move(key), args...);

The C++17 variant improves on the former by not constructing a VeryHeavy if key is already present.

Upvotes: 6

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