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template type's ctor arguments at instantiation time


template type's ctor arguments at instantiation time

By : Vũ Minh Hiếu
Date : January 10 2021, 01:45 PM
I wish this help you
code :


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Issues with constructors for nested class of a template (copy ctor seems to override other ctor)

Issues with constructors for nested class of a template (copy ctor seems to override other ctor)


By : user3073680
Date : March 29 2020, 07:55 AM
wish of those help The const in the copy constructor is important because only lvalues can be bound to non-const references but temporary objects are rvalue and they can't be bound to non-const references. You need to change the signature to;
code :
iterator(const iterator& other) 
Template method with number of arguments fixed for instantiation but variable by template parameter

Template method with number of arguments fixed for instantiation but variable by template parameter


By : Kockaci
Date : March 29 2020, 07:55 AM
Does that help I'd like to define a function for template class with an integer template parameter so that the number of function arguments depends on the template parameter. Here's an example: , You could use the trick that Boost.Hana uses for getNth:
code :
template <typename Coord, int dim, typename = std::make_index_sequence<dim>>
struct Point;

template <typename Coord, int dim, size_t... Ignore>
struct Point<Coord, dim, std::index_sequence<Ignore...>>
{
    void Set(decltype(Ignore, Coord{})... args)
    {
        // ...
    }
};
template <typename... > struct typelist { };

template <int N, typename T, typename = std::make_index_sequence<N>>
struct repeat;

template <int N, typename T>
using repeat_t = typename repeat<N, T>::type;

template <int N, typename T, size_t... Idx>
struct repeat<N, T, std::index_sequence<Idx...>>
{
    template <size_t >
    struct makeT { using type = T; };

    using type = typelist<typename makeT<Idx>::type...>;
};
namespace details {
    template <typename Coord, int dim, typename = repeat_t<dim, Coord>>
    struct Point;

    template <typename Coord, int dim, typename... dimCoords>
    struct Point<Coord, dim, typelist<dimCoords...>>
    {
        void Set(dimCoords... args)
        {

        }
    };
}

template <typename Coord, int dim>
using Point = details::Point<Coord, dim>;
How to write template overload functions with fallback triggered if template arguments do not allow instantiation of a c

How to write template overload functions with fallback triggered if template arguments do not allow instantiation of a c


By : Santiago Castillo
Date : March 29 2020, 07:55 AM
it fixes the issue Remembering your analogue question and the answer from Quentin, I see that the problem is that B can be (apparently) complete when A is incomplete.
The only way I see (sorry: only C++11 at the moment) is impose that the general B is defined only if A is defined (trasforming it in a partial specialization); in the following way
code :
template <typename T, bool = is_complete<A<T>>::value>
struct B;

template <typename T>
struct B<T, true> : A<T>
 { int foo() {return 0;} };

template <>
struct B<bool>
 { int foo() {return 1;} };
#include <iostream>
#include <type_traits>

template <typename T, std::size_t = sizeof(T)>
std::true_type is_complete_impl(T *);

std::false_type is_complete_impl(...);

template <typename T>
using is_complete = decltype(is_complete_impl(std::declval<T*>()));

template <typename>
struct A;

template <>
struct A<int>
 { };

template <typename T, bool = is_complete<A<T>>::value>
struct B;

template <typename T>
struct B<T, true> : A<T>
 { int foo() {return 0;} };

template <>
struct B<bool>
 { int foo() {return 1;} };

template <typename T>
typename std::enable_if<true == is_complete<B<T>>::value, int>::type foo() 
 { B<T> b; return b.foo(); }

template <typename T>
typename std::enable_if<false == is_complete<B<T>>::value, int>::type foo() 
 { return 2; }

int main()
 {
   std::cout << foo<int>() << "\n";     // print 0
   std::cout << foo<bool>() << "\n";    // print 1
   std::cout << foo<double>() << "\n";  // print 2
 }
Issue warning on template instantiation based on template arguments

Issue warning on template instantiation based on template arguments


By : user2346425
Date : March 29 2020, 07:55 AM
may help you . We want to issue a compiler warning, if a user of our headers instantiates a template with certain templated types, which we did so far by template specialization: , Use the attribute on the alias:
code :
template <typename T>
struct  select_container<T, std::deque> {
  using _t [[deprecated("We won't stop you from using deque, but please think twice "
               "(link to wiki).")]] = std::deque<T>;  // custom allocator should also go here
};
Visual C++ cannot deduce given(!) template arguments for function used as default value in ctor

Visual C++ cannot deduce given(!) template arguments for function used as default value in ctor


By : Dmitry
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , Breaking news
After reporting the issue on Clang 3.2, it appears this is actually a C++ defect. You see the bug discussion in the clang database.
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