Suggest use of constexpr constructor when possible

Clean Code New rules / language support
1

It would be helpful if sonarsource would suggest to set a constructor as a constexpr constructor when possible. It would allow the constructor to return a value computed at compile time when requested. It wouldn’t break normal usage of the constructor, just allow more usages.

This feature, and the constraints are described here:

Constexpr constructors (C++11) - IBM Documentation

constexpr specifier (since C++11) - cppreference.com

Example of non compliant code:

    struct IMAGEHELPER_API Color
    {
        Color() noexcept = default;
        explicit Color(uint16_t g) noexcept
            : gray(g) {}
        Color(uint16_t g, uint16_t a) noexcept
            : gray(g), alpha(a) {}
        Color(uint16_t r, uint16_t g, uint16_t b) noexcept
            : red(r), green(g), blue(b) {}
        Color(uint16_t r, uint16_t g, uint16_t b, uint16_t a) noexcept
            : red(r), green(g), blue(b), alpha(a) {}

        uint16_t gray = 0;
        uint16_t red = 0;
        uint16_t green = 0;
        uint16_t blue = 0;
        uint16_t alpha = 0;
    };

That would give the following compliant code:

struct IMAGEHELPER_API Color
    {
        constexpr Color() noexcept = default;
        explicit constexpr Color(uint16_t g) noexcept
            : gray(g) {}
        constexpr Color(uint16_t g, uint16_t a) noexcept
            : gray(g), alpha(a) {}
        constexpr Color(uint16_t r, uint16_t g, uint16_t b) noexcept
            : red(r), green(g), blue(b) {}
        constexpr Color(uint16_t r, uint16_t g, uint16_t b, uint16_t a) noexcept
            : red(r), green(g), blue(b), alpha(a) {}

        uint16_t gray = 0;
        uint16_t red = 0;
        uint16_t green = 0;
        uint16_t blue = 0;
        uint16_t alpha = 0;
    };

Example:

std::unique_ptr has a constexpr constructor:

std::unique_ptr<T,Deleter>::unique_ptr - cppreference.com