In this repository there are C++ simple libraries. They are supposed to be very small, max a few hundreds lines. They must cover a specific need of C++ developers.
If you like something just use it! If it does not cover completly what you need let me know, or just branch it and adjust it.
The fist library is value_or, just one function. It is similar to the std::optional.value_or: it returns the the first paramter not null, if it does not find it, then it returns a default value. It is very similar to a coalesce SQL function.
value_or(T&& default_value, Args&&... to_test_v).It looks for a not null value in to_test_v. If it does not find it, then value_or returns default_value.
Here an example
#include <optional>
#include <vector>
#include <iostream>
#include "value_or.h"
int main()
{
int i = 5;
int* pi = &i;
std::optional<int> o = 12;
std::unique_ptr<int> up = std::make_unique<int>(3);
std::shared_ptr<int> sp = std::make_shared<int>(4);
std::weak_ptr<int> wp = sp;
int r = s4::value_or(10, nullptr, pi, o, up, sp, wp);
std::cout << r << std::endl; // prints 5 because the 1st pointer not null is pi, 10 is the default value
std::vector<int> ints{ 0,1,2,3,4,5 };
std::unique_ptr<std::vector<int>> upv = std::make_unique<std::vector<int>>();
std::unique_ptr<std::vector<int>> upvn;
size_t r2 = s4::value_or(ints, upvn).size();
std::cout << r2 << std::endl; // prints 6, the size of ints, the default value because upwn is null
size_t r3 = s4::value_or(ints, upvn, upv).size();
std::cout << r3 << std::endl; // prints 0, the size of upv
auto l = []() noexcept -> int*
{
return nullptr;
};
const int r4 = s4::value_or(10, l, pi);
std::cout << r4 << std::endl; // prints 5, the value of *pi
std::vector<record> s{
{10, {}},
{{}, 20},
{{}, {}}
};
int r5 = std::accumulate(s.begin(), s.end(), 0,
[](int i, const record& r) { return i + s4::value_or(0, r.v1, r.v2); });
std::cout << r5 << std::endl; // prints 30
}