使用支撑初始化程序列表时,模板参数推导失败 [英] Template argument deduction fails when using braced initializer list
问题描述
我正在尝试在'perpendicular()'函数中使用模板参数推导:
I'm trying to use template argument deduction in the 'perpendicular()' function:
#include <iostream>
template <typename component = double>
struct offset {
component x;
component y;
};
template <typename component>
offset(component x, component y) -> offset<component>;
template <typename component>
offset<component> perpendicular(offset<component> const &o) {
return offset{o.y, -o.x};
}
template <typename component>
std::ostream &operator<<(std::ostream &s, offset<component> const &o) {
return s << '(' << o.x << ", " << o.y << ')';
}
int main() {
std::cout << perpendicular({3.1, 1.2}) << '\n';
return 0;
}
但是,它不能编译;叮当声(带有 -std ='c ++ 17'
)说:候选模板被忽略:无法推断模板参数'component'offset< component>Vertical(offset< component> const& o){
.
This however doesn't compile; Clang (with -std='c++17'
) says: candidate template ignored: couldn't infer template argument 'component' offset<component> perpendicular(offset<component> const &o) {
.
我应该辞职写 perpendicular(offset {1.0,2.0})
还是有办法给编译器一个提示?
Should I resign to writing perpendicular(offset{1.0, 2.0})
or is there a way to give the compiler a hint?
推荐答案
带有 {/*..*/}
的问题是它没有类型,并且大多数只能推导为 std :: initializer_list< T>
或 T [N]
.
Issue with {/*..*/}
is that it has no type, and can mostly only be deduced as std::initializer_list<T>
or T[N]
.
因此,下面将允许所需的语法:
So following would allow desired syntax:
template <typename component>
offset<component> perpendicular(component const (&o)[2]) {
return offset{o[1], -o[0]};
// return perpendicular(offset{o[0], o[1]});
}
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