如何在C#中声明编译时常量函数

Question

在C++中,我们可以使用宏或constexpr(如C++ 11所述).我们在C#中可以做些什么？

有关上下文,请参阅"无法声明..."注释:

static class Constant
{
    // we must ensure this is compile time const, have to calculate it from ground...
    public const int SIZEOF_TEXUTRE_RGBA_U8C4_640x480 = 4 * sizeof(byte) * 640 * 480;

    // Cannot declare compile time constant as following in C#
    //public const int SIZEOF_TEXUTRE_RGBA_U8C4_640x480_2 = 4 * PixelType._8UC4.PixelSize() * 640 * 480;
}

public static class PixelTypeMethods
{
    public static /*constexpr*/ int PixelSize(this PixelType type)
    {
        int value = (int)type;
        int unit_size = value & 0xFF;
        int unit_count = (value & 0xFF00) >> 8;
        return unit_count * unit_size;
    }
}

[Flags]
public enum PixelType
{
    RGBA_8UC4 = RGBA | _8U | _C4,

    /////////////////////////
    RGBA = 1 << 16,

    /////////////////////////
    _8UC4 = _8U | _C4,

    /////////////////////////
    _C4 = 4  << 8,

    /////////////////////////
    _8U = sizeof(byte)
}

Answer 1

要声明一个constant(const),赋值必须是一个编译时常量.自动调用方法使其不是编译时常量.

另一种方法是使用static readonly:

public static readonly int SIZEOF_TEXUTRE_RGBA_U8C4_640x480_2 =
    4 * PixelType._8UC4.PixelSize() * 640 * 480;