CODEWITHSUNDEEP
c++algorithmvectormove-semanticsstd
Magix
Magix

Reputation: 5339

remove_if without the need of move and copy semantics

Here is what a typical vector remove-erase operation looks like :

auto toErase = std::remove_if(vec.begin(), vec.end(),
   [val](obj_t const& obj) { return obj.myval == val; }
); // This actually moves objects around !

vec.erase(toErase, vec.end());

This works fine in the majority of cases, but I am faced with the case where obj_t type does not allow move or copy semantics. Objects are inserted with vec.emplace_back(), and I am looking for an alternative to remove_if that doesn't need either copy or move.

Does it already exist somewhere ? If not, how would it be built ?

Upvotes: 0

Views: 938

Answers (2)

Ihor Drachuk
Ihor Drachuk

Reputation: 1293

It is not possible to remove from std::vector without copy or move support: how will you handle case, when you delete something from the middle? You can use for example std::list<Class> or std::vector<std::shared_ptr<Class>> instead of std::vector<Class>.

Actually, if the main problem around remove_if: I recommend you use shared_ptr or unique_ptr

Upvotes: 3

ALX23z
ALX23z

Reputation: 4713

If object is non-movable/copyable how do you expect to rearrange objects in the vector? Vector is a contiguous container - so you cannot erase an element in the middle without shifting the ending.

To resolve the issue, either make the object movable/copyable, wrap it in unique_ptr (thus making it movable), or use one of map/set/unordered_map containers as those don't relocate objects unlike std::vector

Upvotes: 5

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