how to make explicit conversions from a native type to a user defined type in a template

Question

I want to get a class to be flexible enough to handle explicit conversion based on the typename type in a template. How can it be done? I am guessing the class will have to handle the conversion

Note this may seem like a lot of code to slog through, but I kept it as short as I could.

Here is what I would like to do.

template<typename T> void fooAndBar(T x)
{
    uint64_t count = 0;

    //i want next line to work for x being either uint64_t or bigNumber
    while( x <= (T)1000 ) {
        count++;//do something
    }
}

int main() {

    uint64_t y = 1;
    fooAndBar(y);

    bigNumber z;
    fooAndBar(z);

    return 0;
}

with bigNumber defined as:

#include <vector>

typedef unsigned long long int uill;

class bigNumber //just a class that can handle reaaaly big numbers very striped down
{
public:
    bigNumber();
    ~bigNumber() {}
    bool operator<=(bigNumber rightSide);
    template<typename T> static bigNumber convertToBigNumber(T in);
private:
    std::vector<uill> digits; 
};

bigNumber::bigNumber() { digits.push_back(1); }

bool bigNumber::operator<=(bigNumber rightSide) {
    // dummy function
    return digits.back() <= rightSide.digits.back();
}

template<typename T> static bigNumber bigNumber::convertToBigNumber(T in) {
    bigNumber bn;
    bn.digits.push_back(in);
    return bn;
}

but I am stuck wring separate functions. One for uint64_t and one for bigNumber like so

void foo(uint64_t x) {

    uint64_t count = 0;

    // NB  x is an uint64_t
    while( x <= 1000 ) {
        count++;//do something
    }
}

void bar(bigNumber x) {

    uint64_t count = 0;

    // NB x is a bigNumber
    while( x <= bigNumber::convertToBigNumber(1000) ) {
        count++;//do something
    }
}

int main() {

    uint64_t y=1;
    foo(y);

    bigNumber z ;
    bar(z);

    return 0;
}

Thanks in advance for any help. And this question needs better tags any suggestions would help.

Answer 1

C++ can handle a implicit conversion from int to bigNumber. All you need to do is to add constructor for this case:

C++11:

bigNumber(uill e) : digits{e} {}

C++98:

bigNumber(uill e) { digits.push_back(e); }

and you will be good to go.