Intro

It has come to my attention recently where I would really like to use a constrained vector type. Since C++ is typed language it does not make any sense to often validate the input data into a function for example. An input parameter in a function should be the correct type and shouldn't need validation, in my opinion.

Objective

std::vector wrapper with additional template argument declaring the constraining relationship to the vector. Seamless integration to current code, so you shouldn't need to put much effort in refactoring.

Usage

All of the below code is from the example.cpp file.

Declare a constraining relationship

Make a struct with a callable bool operator,

struct constrain_less_than_20 {
    bool operator()(int value) {
        return value < 20;
    }
};
using lessthan20 = nonstd::vector_constrained<int, std::allocator<int>, constrain_less_than_20>;

Construct vector_constrained from std::vector

std::vector<int> normal_vector{10, 11, 12, 13, 14};
lessthan20 third_vector{normal_vector};

Most of std::vector member functions are implemented

lessthan20 second_vector{first_vector};// copy the first_vector
second_vector.assign({10, 11});// overwrite vector values
second_vector.insert(second_vector.end(), {12, 13});
second_vector.push_back(14);

Implicit conversion to std::vector

void print(const std::vector<int>& vec) {
    for (const auto& item : vec) {
        printf("Item is %d\n", item);
    }
}
int main() {
    lessthan20 third_vector{normal_vector};
    print(third_vector);
}

Known flaws

• All functions in std::vector where iterator is returned has either been commented or changed to const_iterator.