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.
|
1 |
#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.
|
1 2 3 |
// 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.
|
1 2 3 |
// attributes of a specimen STRONG(Height, Mm ) ; STRONG(Weight, Kg ) ; |
Ah OK, here is the first duck flying in. Lets take care of it.
|
1 2 3 4 5 6 7 8 |
// 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
|
1 |
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:
|
1 |
struct Duck { double h; double w ; } |
One can say: “Strong Duck” typing indeed :)
https://cppx.godbolt.org/z/rWW5zI
