在C ++中以在编译时和运行时都可用的方式描述像素格式信息

使用非类型引用模板参数可能是一种解决方案。请参阅http://en.cppreference.com/w/cpp/language/template_parameters。例如这样：

#include <iostream>
#include <cstdint>
#include <array>

enum class color_space : std::uint8_t { rgb, cymk, other };

// PIXEL LAYOUT
// Can be created/modified at runtime, but a predefined set of pixel_layouts
// exists for compile-time use.
struct pixel_layout {
    color_space space;
    std::uint8_t channels;
};

constexpr bool operator==(const pixel_layout& a, const pixel_layout& b) {
    return (a.space == b.space) && (a.channels == b.channels);
}
constexpr bool operator!=(const pixel_layout& a, const pixel_layout& b) {
    return (a.space != b.space) || (a.channels != b.channels);
}

// Predefined pixel_layout instances, for use as template arguments
// As static constexpr members of class, to make sure they have external linkage,
// required for use as reference template arguments.
struct default_pixel_layouts {
    static constexpr pixel_layout rgb{ color_space::rgb, 3 };
    static constexpr pixel_layout cymk{ color_space::cymk, 4 };        
};

// Definitions for the pixel_layouts
constexpr pixel_layout default_pixel_layouts::rgb;
constexpr pixel_layout default_pixel_layouts::cymk;


// PIXEL TYPE
// Takes pixel_layout reference as non-type template argument.
template<const pixel_layout& Layout>
struct pixel {
    static constexpr const pixel_layout& layout = Layout;

    // Because layout is constexpr, can use its members (e.g. channels),
    // for example as template argument.
    // Here size of pixel depends on number of channels in pixel_layout
    std::array<std::uint32_t, layout.channels> data;
};

// RGB and CYMK pixel_types as type aliases
using rgb = pixel<default_pixel_layouts::rgb>;
using cymk = pixel<default_pixel_layouts::cymk>;


// IMAGE
// Takes pixel type as template argument.
template<class PixelType>
class image {
public:
    using pixel_type = PixelType;
};


// TRANSFORM
// Takes pixel_layouts to transform from/to at runtime. Can for with the predefined
// ones, but also with new ones creates at runtime.
class transform {
private:
    const pixel_layout& from_;
    const pixel_layout& to_;

public:
    transform(const pixel_layout& from, const pixel_layout& to) :
    from_(from), to_(to) { }

    // Example: function working on an image
    template<class Image>
    void run(Image& img) {
        // Need to make sure that Image's pixel_layout (compile-time) matches
        // pixel_layout of the transform (runtime).
        if(Image::pixel_type::layout != from_)
            std::cout << "Wrong pixel type on input image" << std::endl;
        else
            std::cout << "transforming..." << std::endl;
    }

};



int main() {
    image<rgb> rgb_img;
    image<cymk> cymk_img;

    // Transform from rgb to cymk
    transform tr(default_pixel_layouts::rgb, default_pixel_layouts::cymk);  
    tr.run(rgb_img); // ok
    tr.run(cymk_img); // error: input to run() must have rgb pixel_layout

    // Creating a new pixel_layout at runtime
    pixel_layout custom_layout = { color_space::other, 10 };
    transform tr2(custom_layout, default_pixel_layouts::cymk);  

    return 0;
}

http://coliru.stacked-crooked.com/a/981e1b03b3b815c5

对于pixel_layout在编译时使用的用例，pixel_layout需要将不同的可用实例实例化为全局静态constexpr对象。

pixel_type然后实例化为不同的类，具体取决于pixel_layout&给定的模板参数。

但是它们仍然可以在运行时使用。