问题描述
我有一个称为 quotient_ring 的通用模结构.相关位如下所示.
I have a generalized modulo struct called quotient_ring. The relevant bits are shown below.
template <typename R = long long>
struct quotient_ring{
using Q = quotient_ring;
R x, m;
...
template <typename T>
friend constexpr std::basic_ostream<T> &operator<< (std::basic_ostream<T> &str, const Q &q){
return str << '(' << q.x << ")%(" << q.m << ')';
}
};
此运算符<< 会将 2 mod 7 之类的内容打印为(2)％(7).我需要括号的原因是因为 R 类型可以变得非常嵌套.但是，如果 R 只是一种算术类型，例如 long long ，我想在不带括号的情况下进行打印.我发现实现此目的的一种方法如下.
This operator << would print something like 2 mod 7 as (2)%(7). The reason I need the brackets is because the type R can become very nested. However, if R is only an arithmetic type, such as long long, I would like to print without the brackets. I found that one way to accomplish this is as follows.
template <typename T>
friend constexpr std::basic_ostream<T> &operator<< (std::basic_ostream<T> &str, const Q &q){
if constexpr (std::is_arithmetic<R>::value) return str << q.x << '%' << q.m;
else return str << '(' << q.x << ")%(" << q.m << ')';
}
我认为这是一个很好的解决方案.但是，我想知道是否可以通过模板专门化来实现相同的目的.我个人更喜欢模板专业化，而不是分支于类型特征.
I think this is a fine solution. However, I would like to know if the same can be achieved by means of template specialization. I tend to personally like template specialization more than branching on type traits.
推荐答案
为什么?如果constexpr 是编译时分支.等效的SFINAE的可读性要差得多.
Why? if constexpr is a compile-time branch. The equivalent SFINAE is far less readable.
template <typename R = long long>
struct quotient_ring{
using Q = quotient_ring;
R x, m;
template <typename Char>
friend constexpr std::enable_if_t<
std::is_arithmetic_v<R>,
std::basic_ostream<Char> &
>
operator<< (std::basic_ostream<Char> &str, const Q &q){
return str << q.x << '%' << q.m;;
}
template <typename Char>
friend constexpr std::enable_if_t<
!std::is_arithmetic_v<R>,
std::basic_ostream<Char> &
>
operator<< (std::basic_ostream<Char> &str, const Q &q){
return str << '(' << q.x << ")%(" << q.m << ')';
}
};
int main() {
quotient_ring<quotient_ring<>> ring{
{1, 2},
{3, 4}
};
std::cout << ring << '\n'; // (1%2)%(3%4)
}
我建议您在输出中添加一些空格(例如(1％2)％(3％4))以使其更具可读性吗?
Might I suggest putting some spaces in the output (like (1 % 2) % (3 % 4)) to make it more readable?
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