Sir Jony Sir Jony - 1 month ago 12
C++ Question

Constructor Overloading Ambiguity When Trying to Support Literals

Code



#include <iostream>

template <typename Type>
class MyContainer
{
private:
Type contained;
public:
MyContainer<Type>(Type & a): contained(a) { std::cout << "&\n"; }
MyContainer<Type>(Type a): contained(a) { std::cout << "_\n"; }
};

class Epidemic
{
private:
int criticality;
public:
Epidemic(int c): criticality(c);
};

int main()
{
// using objects //
Epidemic ignorance(10);
MyContainer<Epidemic> testtube(ignorance); // should print "&"; error instead

// using primitive //
double irrationalnumber = 3.1415;
MyContainer<double> blasphemousnumber(irrationalnumber); // should print "&"; error instead

// using literal //
MyContainer<double> digits(123456789.0); // prints "_"
}





Description



MyContainer<Type>(Type & a)
is meant for most everything. However, it won't work with literals (e.g.
1.732
). That's why I added a
MyContainer<Type>(Type a)
. However, by adding this, I end up with an ambiguity because non-literals can use either constructor.




Question




Is there a way to satisfy all parameters (both literal and non-literal) given to a constructor?

Answer

Just change from the value type parameter to a const reference:

template <typename Type>
class MyContainer
{
private:
    Type contained;
public:
    MyContainer<Type>(Type & a): contained(a) { std::cout << "&\n"; }
    MyContainer<Type>(const Type& a): contained(a) { std::cout << "_\n"; }
                   // ^^^^^     ^
};
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