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How negate std::is_integral for use in tag dispatch?


How negate std::is_integral for use in tag dispatch?

By : Bhumika Gunjal
Date : November 26 2020, 01:01 AM
fixed the issue. Will look into that further you may instantiate a std::integral_constant from a constexpr value like this:
code :


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Differences between std::is_integer and std::is_integral?

Differences between std::is_integer and std::is_integral?


By : user5739406
Date : March 29 2020, 07:55 AM
hope this fix your issue std::is_integer does not exist.
That being said, std::numeric_limits::is_integer does exist.
How do I use std::is_integral<> to select an implementation?

How do I use std::is_integral<> to select an implementation?


By : Chirag Soni
Date : March 29 2020, 07:55 AM
With these it helps Function templates cannot be partially specialized and, in general, it is not a good idea to use function template specialization.
One way to achieve what you want is to use a technique called tag dispatching, which basically consists in providing a forwarder function that selects the right overload based on the value of an extra dummy argument:
code :
#include <type_traits>
#include <cstdint>

template<class T>
int64_t to_int64t( const T& t, std::true_type )
{
    return t;
}

template<class T>
int64_t to_int64t( const T& t, std::false_type )
{
    return t.to_int64t();
}

template<class T>
int64_t to_int64t( const T& t )
{
    return to_int64t(t, std::is_integral<T>());
}

int main()
{
    int64_t i = 64;
    auto x = to_int64t( i );
}
#include <type_traits>
#include <cstdint>

template<class T, typename std::enable_if<
    std::is_integral<T>::value>::type* = nullptr>
int64_t to_int64t( const T& t )
{
    return t;
}

template<class T, typename std::enable_if<
    !std::is_integral<T>::value>::type* = nullptr>
int64_t to_int64t( const T& t )
{
    return t.to_int64t();
}

int main()
{
    int64_t i = 64;
    auto x = to_int64t( i );
}
#include <type_traits>
#include <cstdint>

namespace detail
{
    template<class T, bool = std::is_integral<T>::value>
    struct helper { };

    template<class T>
    struct helper<T, true>
    {
        static int64_t to_int64t( const T& t )
        {
            return t;
        }
    };

    template<class T>
    struct helper<T, false>
    {
        static int64_t to_int64t( const T& t )
        {
            return t.to_int64t();
        }
    };
}

template<class T>
int64_t to_int64t( const T& t )
{
    return detail::helper<T>::to_int64t(t);
}

int main()
{
    int64_t i = 64;
    auto x = to_int64t( i );
}
is_integral vs is_integer: is one of them redundant?

is_integral vs is_integer: is one of them redundant?


By : Bala Krishnan M
Date : March 29 2020, 07:55 AM
will help you std::numeric_limits::is_integer was not introduced by C++11. It was just updated to use the new constexpr qualifier.
std::is_integral was introduced by C++11, and you're right it gives the same results. As to why it was added - possibly because the integral-ness or otherwise of a type isn't logically part of that type's numeric_limits?
How is std::is_integral implemented?

How is std::is_integral implemented?


By : 朱文超
Date : March 29 2020, 07:55 AM
this one helps. From here we have that:
code :
template<typename> struct is_integral_base: std::false_type {};

template<> struct is_integral_base<bool>: std::true_type {};
template<> struct is_integral_base<int>: std::true_type {};
template<> struct is_integral_base<short>: std::true_type {};

template<typename T> struct is_integral: is_integral_base<std::remove_cv_t<T>> {};

// ...
Why does is_integral think that std::string is integral?

Why does is_integral think that std::string is integral?


By : Menahem Shapira
Date : March 29 2020, 07:55 AM
Does that help C++ don't allow you to have ill formed code. Let's take a simple example:
code :
int i = 0;
if constexpr (sizeof(int) > 98) { // never happen
    i = "a string";
}
[](auto) { // this is a template
    int i = 0;
    if constexpr (sizeof(int) > 98) { // never happen
        i = "a string"; // same error
    }
}
[](auto a) { // this is a template
    if constexpr (sizeof(a) > 98) { // maybe happen
        a = "a string"; // no error?
    }
}
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