C++ 向后推以将临时容器添加到另一个容器
我正在编写一个C++ 向后推以将临时容器添加到另一个容器,c++,templates,c++11,template-meta-programming,C++,Templates,C++11,Template Meta Programming,我正在编写一个push_back函数,用于将临时容器添加到另一个容器中 在使用push_-back之前,它应该调整容器的大小或保留容器(如果两者都可用,它也应该选择保留而不是调整大小) 目前的代码是: namespace detail { template<class> struct sfinae_true : std::true_type{}; template<class T, class A0> static auto test_r
push_back
函数,用于将临时容器添加到另一个容器中
在使用push_-back之前,它应该调整容器的大小或保留容器(如果两者都可用,它也应该选择保留而不是调整大小)
目前的代码是:
namespace detail
{
template<class>
struct sfinae_true : std::true_type{};
template<class T, class A0>
static auto test_reserve(int)
->sfinae_true<decltype(std::declval<T>().reserve(std::declval<A0>()))>;
template<class, class A0>
static auto test_reserve(long)->std::false_type;
template<class T, class A0>
static auto test_resize(int)
->sfinae_true<decltype(std::declval<T>().resize(std::declval<A0>()))>;
template<class, class A0>
static auto test_resize(long)->std::false_type;
}
//check if class T have reserve(Arg) function
template<class T, class Arg>
struct HasReserve : decltype(detail::test_reserve<T, Arg>(0)){};
//check if class T have resize(Arg) function
template<class T, class Arg>
struct HasResize : decltype(detail::test_resize<T, Arg>(0)){};
//enable if resize function exists and there is no reserve function
template<class T1, class T2>
typename std::enable_if<HasResize< T1, typename T1::size_type>::value &&
(!HasReserve< T1, typename T1::value_type>::value), void>::type
inline reserveOrResize(T1& dst, T2&& src, typename T2::size_type newSize){
static_assert(std::is_lvalue_reference<T1&>::value, "You must pass lvalue_refrence as first parameter");
static_assert(std::is_rvalue_reference<T2&&>::value, "You must pass rvalue_refrence as second parameter");
int loc = dst.size() + 1;
dst.resize(newSize);
std::cout << "Resizing\n";
for (auto&& elem : src){
dst[loc++] = std::move(elem);
}
}
//enable if reserve function exists
template<class T1, class T2>
typename std::enable_if<HasReserve< T1, typename T1::size_type>::value, void>::type
inline reserveOrResize(T1& dst, T2&& src, typename T2::size_type newSize){
static_assert(std::is_lvalue_reference<T1&>::value, "You must pass lvalue_refrence as first parameter");
static_assert(std::is_rvalue_reference<T2&&>::value, "You must pass rvalue_refrence as second parameter");
dst.reserve(newSize);
std::cout << "Reserving\n";
for (auto&& elem : src){
dst.push_back(std::move(elem));
}
}
//push_back container T2 at the end of Container T1
//T2 must be rvalue refrence
template<class T1, class T2>
void push_back(T1& dst, T2&& src){
static_assert(std::is_lvalue_reference<T1&>::value, "You must pass lvalue_refrence as first parameter");
static_assert(std::is_rvalue_reference<T2&&>::value, "You must pass rvalue_refrence as second parameter");
reserveOrResize(dst, std::move(src), src.size());
}
名称空间详细信息
{
模板
结构sfinae_true:std::true_type{};
模板
静态自动测试备用(int)
->错误在这里
(!HasReserve< T1, typename T1::value_type>::value), void>::type
(!hasreference::value),void>:type
应该是typename T1::size\u type
,而不是value\u type
,因为使用value\u type
您试图检查,该容器具有类型为T1::value\u type
的参数的方法保留(在您的情况下是结构A
),因为在vector中没有这样的方法,所以这两个函数都可用
struct A{};
int main(){
std::vector<A> vec;
push_back(vec,std::vector<A>(10));//error
}
main.cpp: In instantiation of 'void push_back(T1&, T2&&) [with T1 = std::vector<A> T2 =
std::vector<A>]':
main.cpp:74:35: required from here
main.cpp:67:49: error: call of overloaded 'reserveOrResize(std::vector<A>&, std::remove_reference<std::vector<A>&>::type, std::vector<A>::size_type)' is ambiguous
reserveOrResize(dst, std::move(src), src.size());
^
main.cpp:67:49: note: candidates are:
main.cpp:37:9: note: typename std::enable_if<(HasResize<T1, typename T1::size_type>::value && (! HasReserve<T1, typename T1::value_type>::value)), void>::type reserveOrResize(T1&, T2&&, typename T2::size_type) [with T1 = std::vector<A> T2 = std::vector<A> typename std::enable_if<(HasResize<T1, typename T1::size_type>::value && (! HasReserve<T1, typename T1::value_type>::value)), void>::type = void; typename T2::size_type = long unsigned int]
inline reserveOrResize(T1& dst, T2&& src, typename T2::size_type newSize){
^
main.cpp:51:8: note: typename std::enable_if<HasReserve<T1, typename T1::size_type>::value, void>::type reserveOrResize(T1&, T2&&, typename T2::size_type) [with T1 = std::vector<A> T2 = std::vector<A> typename std::enable_if<HasReserve<T1, typename T1::size_type>::value, void>::type = void; typename T2::size_type = long unsigned int]
inline reserveOrResize(T1& dst, T2&& src, typename T2::size_type newSize){
^
(!HasReserve< T1, typename T1::value_type>::value), void>::type