How to use remove_if on an std::vector of std::unique_ptr? [duplicate]

Question

I'm trying to remove_if a vector of unique_ptr. Having forgotten to have my lambda not attempt to copy parameters, I searched for the explanation and found it in Can you use `std::remove_if` on a container of `std::unique_ptr`?.

But when I attempt to pass my lambda parameter by reference or const ref as advised there and in other questions on the matter, I still get 'std::unique_ptr<int,std::default_delete<int>>::unique_ptr(const std::unique_ptr<int,std::default_delete<int>> &)': attempting to reference a deleted function. I don't get why this copy construct would be called.

std::vector<std::unique_ptr<int>> v { std::make_unique<int>(1), std::make_unique<int>(2), std::make_unique<int>(3) }; auto result = std::remove_if(v.begin(), v.end(), [](const std::unique_ptr<int> &it) {return *it > 2; });

What am I missing ?

Issue is vector initialization... you cannot use initializer_list here :/ — Jarod42
– Jarod42, Commented May 19, 2021 at 14:34

Caleth · Accepted Answer · 2021-05-19 14:34:53Z

What am I missing ?

It's complaining about the construction, not the use.

std::initialiser_list can only be copied from, so std::initialiser_list<std::unique_ptr<...>> is useless.

#include <memory> #include <vector> #include <algorithm> int main() { std::vector<std::unique_ptr<int>> v; v.emplace_back(std::make_unique<int>(1)); v.emplace_back(std::make_unique<int>(2)); v.emplace_back(std::make_unique<int>(3)); auto result = std::remove_if(v.begin(), v.end(), [](const std::unique_ptr<int> &it) {return *it > 2; }); v.erase(result, v.end()); }

See it on coliru

Relevant quote: The underlying array is a temporary array of type const T[N], in which each element is copy-initialized (except that narrowing conversions are invalid) from the corresponding element of the original initializer list.

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