f32 pack_color_cast(u8 r, u8 g, u8 b, u8 a = 255)
{
    u32 raw = (a << 24) | (b << 16) | (g << 8) | r;
    return *cast(f32*)&raw;
}

f32 pack_color_union(u8 r, u8 g, u8 b, u8 a = 255)
{
    union RawValue { f32 value; u32 raw; }
    RawValue rv = void;
    rv.raw = (a << 24) | (b << 16) | (g << 8) | r;
    return rv.value;
}

enum RED  = pack_color_cast(1.0, 0.0, 0.0, 1.0);    // OK
enum BLUE = pack_color_union(1.0, 0.0, 0.0, 1.0);  // Error: reinterpretation through overlapped field value is not allowed in CTFE