Compile-time binary conversion with variadic templates

binary-converter.cc

#include <iostream>
#include <type_traits>
#include <cassert>

namespace details {
    template<typename T> struct DigitValue {
    };

    template<> struct DigitValue<int> {
        static constexpr int v(const int value) { return value; }
    };

    template<> struct DigitValue<char> {
        static constexpr int v(const char value) { return value - '0'; }
    };
}

template<unsigned Result, typename Vals, Vals ...digits> struct BinaryConverterBase {
};

template<unsigned Result, typename Vals, Vals Head, Vals ...Tail> 
struct BinaryConverterBase<Result, Vals, Head, Tail...> {
    static constexpr unsigned value = BinaryConverterBase<2 * Result + details::DigitValue<Vals>::v(Head), 
                                                          Vals, Tail...>::value;
};

template<unsigned Result, typename Vals> struct BinaryConverterBase<Result, Vals> {
    static constexpr unsigned value = Result;
};

template<typename T, T ...digits> struct BinaryConverter : public BinaryConverterBase<0, T, digits...>
{
};


template<char ...digits> constexpr unsigned operator"" _b() {
    return BinaryConverter<char, digits...>::value;
}

static_assert(BinaryConverter<0>::value == 0, "0b != 0");
static_assert(BinaryConverter<0, 1, 1, 1>::value == 7, "0111b != 7");
static_assert(BinaryConverter<1, 0, 1, 1>::value == 11, "1011b != 11");

static_assert(BinaryConverter<char, '0'>::value == 0, "0b != 0");
static_assert(BinaryConverter<char, '0','1', '1', '1'>::value == 7, "0111b != 7");
static_assert(BinaryConverter<char, '1', '0', '1', '1'>::value == 11, "1011b != 11");

int main() {
    assert(0111_b == 0x7);
    assert(11111111_b == 0xFF);
    assert(10101010_b == 0xAA);
}