Question: I can create a C++11 Template function to explicitly convert a bitset into an unsigned long:

```
template<size_t N>
unsigned long U(bitset<N> x) {
    return x.to_ulong();
}

// Explicit conversion
unsigned long y = U(bitset<4>("1010"));

```

Is there a way to "implicitly" convert bitset to an unsigned long using a C++11 template helper function. For Example, if I assign a bitset to an unsigned long, then I want it to automatically convert the bitset to the correct type:

```
// What Template Function in C++11?

// Implicit Conversion
unsigned long z = bitset<4>("1010");

```

(If its not possible to create an implicit convertion rule to convert to "unsigned long using a C++11 template function, its also acceptable to derive a new class from bitset that has casting function to unsigned long. Is that possible as well?)

Answer: 
You could wrap `std::bitset` in your own implicitly convertible class:

```
template<size_t N>
class MyBitset
{
public:
    // constructors elided here

    operator unsigned long()
    {
        return _bitset.to_ulong();
    }

    operator std::bitset<N>()
    {
        return _bitset; // Note that you get a copy here.
    }

private:
    std::bitset<N> _bitset;
};

```

[Demo](https://godbolt.org/g/euuB3f)

If you are trying to derive from non-polymorphic classes in `namespace std` (i.e. those without virtual destructors), you are [not writing idiomatic C++](https://stackoverflow.com/questions/6006860/why-should-one-not-derive-from-c-std-string-class), don't do it. Whether the above is really a solution to your problem we can't tell. If all you need is `unsigned long` constants from your bitstrings, you could skip the class wrapper and replace its constructors with templated functions directly:

```
template<size_t N, class CharT>
unsigned long toUlong(const CharT* str,
                 typename std::basic_string<CharT>::size_type n =
                     std::basic_string<CharT>::npos,
                 CharT zero = CharT('0'),
                 CharT one = CharT('1'))
{
    return std::bitset<N>(str, n, zero, one).to_ulong();
}

```

[Demo](https://godbolt.org/g/YJxJeG)
Another Solution based on Maxim's Bullet 2:

```
template<size_t N>
class bits : public bitset<N> {
public:
    bits(unsigned long num) : bitset<N>(num) {}
    bits(char* binstr) : bitset<N>(binstr){}

    operator unsigned long() {
        return this->to_ulong();
    }

    // Slice Bit Range
    unsigned long slice(unsigned L, unsigned R)
    {
        unsigned long P1;
        unsigned long P2;

        if (L>R) {
            P2 = L;
            P1 = R;
        }
        else {
            P2 = R;
            P1 = L;
        }

        unsigned long x = this->to_ulong();
        unsigned long W = P2 - P1 + 1;

        unsigned long Value = (x >> P1) & ((1<<W) - 1);

        return Value;
    }

    // Return Hex String
    string hstr() {
        stringstream xx;
        xx << "0x" << hex << this->to_ulong();
        return xx.str();
    }
};

int main(int argc, char** argv) {
    // Implicit conversion...
    unsigned long xxx = bits<4>("0101");
    unsigned long yyy = bits<4>(xxx).slice(1, 2);
}

```