I admit. C++ Strong Duck , is a click bait title. Perhaps.
Please first make a slight detour into the direction of “Strong Type by Struct“.
“Just make everything to be a class”. Primordial C++ idea. But, I don’t care if it is. It works. If used but not overused. There is no complex C++ lib behind. Almost nothing. Just the agreement.
Make every “strong type” as one struct, with a single member named ‘v’. Name of the struct is the strong type name. Type of the v is defined by you.
Let the code speak.
#define STRONG(N,T) struct N final { T v; }
This is my minuscule macro, that works for me. We do not want to mix kilograms and millimeters. So lets make them as strong types.
// measurement units
STRONG(Kg, double);
STRONG(Mm, double);
And now we have some creatures to manage. We use the same ridiculously simple macro to produce much cleaner code.
// attributes of a specimen
STRONG(Height, Mm ) ;
STRONG(Weight, Kg ) ;
Ah OK, here is the first duck flying in. Lets take care of it.
// we will call it 'duffy'
// same as every other creature, duffy can not change (morph)
// into some other Duck, even if they are both Duck's
// ditto ...
constexpr struct StrongDuck final {
mutable Height height;
mutable Weight weight;
} duffy { {4.2},{430.23} } ;
Duffy is immutable, but it has gained in weight
duffy.weight = {4.552 };
There are no methods, here, one can indeed mistake height for weight when giving them values, but everybody knows what to do about that.
The point is we have described a Duck as a strong type. Much (much) better than:
struct Duck { double h; double w ; }
One can say: “Strong Duck” typing indeed :)