Range based loop: get item by value or reference to const?

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If you don’t want to change the items as well as want to avoid making copies, then auto const & is the correct choice:

for (auto const &x : vec)

Whoever suggests you to use auto & is wrong. Ignore them.

Here is recap:

  • Choose auto x when you want to work with copies.
  • Choose auto &x when you want to work with original items and may modify them.
  • Choose auto const &x when you want to work with original items and will not modify them.

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