Hi Roomon
Oh right! In that case I think I’ve just not fundamentally understood the linked answer. I assumed that the constructor had been defined fully in line 4 of my header file. I’ll go away and learn more about structs 
As my struct is contained within the class header file, I’m guessing I’ll need to define the constructor in the .cpp file something like
classname::structname structname(uint32 InPriority)
{
...
}