There is already one in C++20: std::ranges::contains (https://en.cppreference.com/w/cpp/algorithm/ranges/contains).

On 23-Dec-2023, at 14:50, Robert Sitton via Std-Proposals <std-proposals_at_[hidden]> wrote:

Dear std-proposals community,

I hope this email finds you well. I am writing to introduce a proposal for the addition of a new utility function, std::contains, to the C++ standard library. This function aims to streamline the common task of checking whether a container contains a specific element and enhance the overall readability of C++ code.

Motivation:
One of the frequent operations in C++ programming involves checking whether a container (e.g., std::vector, std::list, std::set) contains a particular value. While C++ provides mechanisms to achieve this, such as custom loops or std::find, these approaches may not always be as intuitive and efficient as desired.

Proposal Overview:
The proposed std::contains function is designed to simplify this operation and make code more expressive. It offers a straightforward and concise way to check if a container contains a specified element, reducing the need for manual iterations and enhancing code clarity.

Function Signature:
template <typename Container, typename T>
bool std::contains(const Container& container, const T& value);

Example Usage:
std::vector<int> numbers = {1, 2, 3, 4, 5};
bool containsThree = std::contains(numbers, 3); // true
bool containsTen = std::contains(numbers, 10); // false
bool containsOne = std::contains(numbers, {1, 4, 5}); // true
bool containsTwo = std::contains(numbers, {7, 8}); // false

Your Feedback:
I would greatly appreciate your feedback and insights on this proposal. Before formally submitting it to the C++ committee, I believe it is essential to gather input from the community to ensure that the proposal aligns with the needs and expectations of C++ developers.

Please feel free to share your thoughts, suggestions, or concerns regarding the proposed std::contains function. Your expertise and feedback are invaluable in refining and improving this idea. Thank you for your time and attention. I look forward to engaging in constructive discussions and working together to enhance the C++ standard library.

Sincerely,

Robert

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