Constant in separate namespace using class/struct with a big constuctor - c++

Question

I have a struct:
struct ColorspaceData
{
private:
glm::vec3 sMatrix;
public:
/// X red
float xr;
/// Y red
float yr;
/// Z red
float zr;
/// X green
float xg;
/// Y green
float yg;
/// Z green
float zg;
/// X blue
float xb;
/// y blue
float yb;
/// Z blue
float zb;
/// Whitepoint
WhitepointData *whitepoint;
/// A [3x3] matrix used in linear-gamma transformation function
glm::mat3 linearTransform;
/// Result of linear-gamma transformation function as `LinearTransformData`
TransformData *linearTransformData;
ColorspaceData(float c_xr, float c_yr, float c_xg, float c_yg, float c_xb, float c_yb,
StdIlluminant c_whitepoint, TransformData c_linearTransformData)
{
xr = c_xr / c_yr;
xg = c_xg / c_yg;
xb = c_xb / c_yb;
yr = 1.0f;
yg = 1.0f;
yb = 1.0f;
zr = (1.0f - c_xr - c_yr) / c_yr;
zg = (1.0f - c_xg - c_yg) / c_yg;
zb = (1.0f - c_xb - c_yb) / c_yb;
switch (c_whitepoint)
{
case (StdIlluminant::A):
whitepoint = new WhitepointData(0.44757f, 0.40745f);
break;
case (StdIlluminant::B):
whitepoint = new WhitepointData(0.34842f, 0.35161f);
break;
case (StdIlluminant::C):
whitepoint = new WhitepointData(0.31006f, 0.31616f);
break;
case (StdIlluminant::D50):
whitepoint = new WhitepointData(0.34567f, 0.35850f);
break;
case (StdIlluminant::D55):
whitepoint = new WhitepointData(0.33242f, 0.34743f);
break;
case (StdIlluminant::D65):
whitepoint = new WhitepointData(0.31271f, 0.32902f);
break;
case (StdIlluminant::D75):
whitepoint = new WhitepointData(0.29902f, 0.31485f);
break;
case (StdIlluminant::D93):
whitepoint = new WhitepointData(0.28315f, 0.29711f);
break;
case (StdIlluminant::E):
whitepoint = new WhitepointData(0.33333f, 0.33333f);
break;
case (StdIlluminant::F1):
whitepoint = new WhitepointData(0.31310f, 0.33727f);
break;
case (StdIlluminant::F2):
whitepoint = new WhitepointData(0.37208f, 0.37529f);
break;
case (StdIlluminant::F3):
whitepoint = new WhitepointData(0.40910f, 0.39430f);
break;
case (StdIlluminant::F4):
whitepoint = new WhitepointData(0.44018f, 0.40329f);
break;
case (StdIlluminant::F5):
whitepoint = new WhitepointData(0.31379f, 0.34531f);
break;
case (StdIlluminant::F6):
whitepoint = new WhitepointData(0.37790f, 0.38835f);
break;
case (StdIlluminant::F7):
whitepoint = new WhitepointData(0.31292f, 0.32933f);
break;
case (StdIlluminant::F8):
whitepoint = new WhitepointData(0.34588f, 0.35875f);
break;
case (StdIlluminant::F9):
whitepoint = new WhitepointData(0.37417f, 0.37281f);
break;
case (StdIlluminant::F10):
whitepoint = new WhitepointData(0.34609f, 0.35986f);
break;
case (StdIlluminant::F11):
whitepoint = new WhitepointData(0.38052f, 0.37713f);
break;
case (StdIlluminant::F12):
whitepoint = new WhitepointData(0.43695f, 0.40441f);
break;
case (StdIlluminant::LEDB1):
whitepoint = new WhitepointData(0.4560f, 0.4078f);
break;
case (StdIlluminant::LEDB2):
whitepoint = new WhitepointData(0.4357f, 0.4012f);
break;
case (StdIlluminant::LEDB3):
whitepoint = new WhitepointData(0.3756f, 0.3723f);
break;
case (StdIlluminant::LEDB4):
whitepoint = new WhitepointData(0.3422f, 0.3502f);
break;
case (StdIlluminant::LEDB5):
whitepoint = new WhitepointData(0.3118f, 0.3236f);
break;
case (StdIlluminant::LEDBH1):
whitepoint = new WhitepointData(0.4474f, 0.4066f);
break;
case (StdIlluminant::LEDRGB1):
whitepoint = new WhitepointData(0.4557f, 0.4211f);
break;
case (StdIlluminant::LEDV1):
whitepoint = new WhitepointData(0.4560f, 0.4548f);
break;
case (StdIlluminant::LEDV2):
whitepoint = new WhitepointData(0.3781f, 0.3775f);
break;
case (StdIlluminant::Theatre):
whitepoint = new WhitepointData(0.3141f, 0.351f);
break;
default:
throw new ColorException("Undefined whitepoint value");
}
sMatrix = glm::vec3(whitepoint->x, whitepoint->y, whitepoint->z) * glm::inverse(glm::mat3x3(xr, xg, xb, yr, yg,
yb, zr, zg, zb));
linearTransform = glm::mat3(sMatrix[0] * xr, sMatrix[1] * xg, sMatrix[2] * xb,
sMatrix[0] * yr, sMatrix[1] * yg, sMatrix[2] * yb,
sMatrix[0] * zr, sMatrix[1] * zg, sMatrix[2] * zb);
linearTransformData = &c_linearTransformData;
}
};
I need to declare CT variable. It works with #define:
#define ColorspaceDefaultSRGB ColorspaceData(0.64f, 0.33f, 0.3f, 0.6f, 0.15f, 0.06f, StdIlluminant::D65, TransformData(1.055f, 0.0031308f, 12.0f / 5.0f, 12.92f, 0.04045f))
But describing constexpr constructor is too many code duplicate like this (I've got an explanation in my previous question):
constexpr ColorspaceData(float p_xr, float p_yr): xr(p_xr), yr(p_yr) ... (other constructor code) {};
Need to describe all lines twice? Declaring a function for constructor? What is the best way to do that?

Answer 1

I suggest a constexpr init method if you can't make the whole constructor constexpr containing all the code that should be duplicated. Note that if a function is constexpr you can call it even if in that case a non constexpr would work too.
constexpr void init(...){
//a lot of stuff
}
ColorspaceData(...){
init(...)
//not constexpr stuff
}
constexpr ColorspaceData(...){
init(...)
//constexpr stuff
}