Is ther a way to define global constants of a certain class inside this class namespace in C++?

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Imagine I have a C++ struct called Color

struct Color {
    float r,g,b;
};

and a function that accepts a Color object and does something with it:

void func(const Color & color) {...}

Usually, I call this function with Color objects constructed on the fly:

func(Color{0.1,0.2,0.3});

But there are certain colors that I use a lot, for example, black, white and red. So I find myself doing this a lot:

func(Color{0.0,0.0,0.0}); // black
func(Color{1.0,1.0,1.0}); // white
func(Color{1.0,0.0,0.0}); // red

What I would like to do instead is

func(Color::black);
func(Color::white);
func(Color::red);

So I am looking for a way to define global constants of type Color inside the Color namespace. So far, I've tried these two options:

Option 1: define a namespace with the same name as the struct; doesn't work because of conflicting namespaces.

struct Color {
    float r,g,b;
};

namespace Color {
    const Color black{0.0,0.0,0.0};
    const Color white{1.0,1.0,1.0};
    const Color red{1.0,0.0,0.0};
}

Option 2: static variables inside of the struct definition; doesn't work since this makes the struct definition incomplete.

// static members
struct Color {
    float r,g,b;

    static Color red = Color{1.0,0.0,0.0};
};

Is there a way to achieve what I want, or at least something similar?

c++
1 Answers
struct Color {
    float r, g, b;

    static const Color red;
};

constexpr Color Color::red{1.0,0.0,0.0};
user_28053050
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