[英]Does C++ allow normal parameters after variadic template parameters?
According to cppreference , the following code is legal: 根据cppreference ,以下代码是合法的:
lock_guard( MutexTypes&... m, std::adopt_lock_t t );
However, the following code cannot be compiled with clang 3.8 (-std=c++1z): 但是,以下代码无法使用clang 3.8(-std = c ++ 1z)进行编译:
template<typename... Args>
void f(Args&&..., bool)
{}
int main()
{
f(1, 2, 3, true); // error! see below for details.
}
1>main.cpp(59,2): error : no matching function for call to 'f' 1> f(1, 2, 3, true); 1> ^ 1> main.cpp(54,6) : note: candidate function not viable: requires 1 argument, but 4 were provided 1> void f(Args&&..., bool) 1> ^ 1> 1 error generated.
Does C++ allow normal parameters after variadic parameters? 在可变参数之后,C ++是否允许正常参数?
The function declaration in your code is valid, however deduction does not work properly for such function templates. 代码中的函数声明是有效的,但是对于此类函数模板, 演绎不起作用。 Note that the following code is well-formed, and instantiates the specialization
void f(int, int, int, bool)
: 请注意,以下代码格式正确,并实例化了特殊化
void f(int, int, int, bool)
:
template<typename... Args>
void f(Args&&..., bool) {}
int main() {
f<int, int, int>(1, 2, 3, true);
}
Note that in C++17, MutexTypes...
are the template parameters to the class itself: 请注意,在C ++ 17中,
MutexTypes...
是类本身的模板参数:
template <class... MutexTypes> class lock_guard;
so they are known and do not need to be deduced. 所以他们是众所周知的,不需要推断。 Note that the constructor with
adopt_lock_t
cannot be used for C++17 class template argument deduction since the adopt_lock_t
argument occurs after the parameter pack. 请注意,带有
adopt_lock_t
的构造函数不能用于C ++ 17类模板参数推导,因为adopt_lock_t
参数出现在参数包之后。 If the committee had been prescient in C++11, they would have put the adopt_lock_t
argument at the beginning rather than at the end, but alas, it is too late now. 如果委员会在C ++ 11中具有先见之明,那么他们就会把
adopt_lock_t
论点放在开头而不是最后,但唉,现在已经太晚了。
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