CODEWITHSUNDEEP
c++boost
maths soso
maths soso

Reputation: 51

How Can I instantiate a class template without a cast

I would like to run the first instantiation instead of the second, but the compiler takes the arguments as integers and returns errors.

Note that the use of optional is to allow the object to receive a boost::none (C++ version of python's None).

#include <boost/multiprecision/cpp_int.hpp>
#include <boost/optional.hpp>
using namespace boost::multiprecision;

template<class T>
struct Point
{
    explicit Point(T x, T y): x (x), y (y){}
    T x;
    T y;
};

typedef boost::optional<int128_t> oint128_t;
int main(){
    // Point<oint128_t> P(90, 5); // this fails
    Point<oint128_t> Q((oint128_t) 91, (oint128_t) 31); // this works
}

Upvotes: 0

Views: 43

Answers (1)

Silvio Mayolo
Silvio Mayolo

Reputation: 70277

You can always put the explicit casts inside of the Point constructor.

template<typename S>
explicit Point(S x, S y): x(T(x)), y(T(y)) {}

But I suspect that doing so will introduce more confusing type errors in the long run. My recommendation is to explicitly call the boost::optional constructor like you're supposed to. T is not meant to be an instance of boost::optional<T>. The cast you're invoking is actually calling a converting constructor and making a new object; you're just making it look like a conversion is taking place.

Upvotes: 1

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