is_integral与is_integer:其中之一是否多余? [英] is_integral vs is_integer: is one of them redundant?

问题描述

is_integral 和

is_integral and is_integer seem to answer the same thing in the same way.

在相关文档页面的链接中， is_integral 似乎缺少以下类型的专业化

From the links to the related documentation pages, is_integral seems to be missing specializations for the following types

signed char       
unsigned char     
unsigned short    
unsigned int      
unsigned long     
unsigned long long

还有一个编译示例，(当然)还显示了它们在这些类型上的相同行为:

Yet a compiled example, shows (of course) their identical behaviour on those types as well:

#include <iostream>
#include <type_traits>
using namespace std;

int main() 
{
    cout << is_integral<signed char       >::value << endl;
    cout << is_integral<unsigned char     >::value << endl;
    cout << is_integral<unsigned short    >::value << endl;
    cout << is_integral<unsigned int      >::value << endl;
    cout << is_integral<unsigned long     >::value << endl; 
    cout << is_integral<unsigned long long>::value << endl;
    return 0;
}

因此，如果它们的行为也相同，那么在C ++ 11中引入它们的意义何在?

So if they also behave the same, what was the point of introducing both of them in C++11?

因此，如果它们的行为也相同，那么在c ++ 11中引入它们的意义何在?

没用指出，短语包括任何有符号，无符号和cv限定的变体 is_integral 文档页面上的em>表明，即使它们的规范也是完全匹配的.

As Useless points out, the phrase including any signed, unsigned, and cv-qualified variants from the is_integral doc page reveals that even their specifications are a complete match.

推荐答案

std :: numeric_limits< T> :: is_integer 不是C ++ 11引入的.刚刚更新为使用新的 constexpr 限定符.

std::numeric_limits<T>::is_integer was not introduced by C++11. It was just updated to use the new constexpr qualifier.

std :: is_integral< T> 是C ++ 11引入的，您说对了，它给出了相同的结果.至于为什么要添加它-可能是因为某种类型的完整性或逻辑上不是该类型 numeric_limits 的一部分?

std::is_integral<T> was introduced by C++11, and you're right it gives the same results. As to why it was added - possibly because the integral-ness or otherwise of a type isn't logically part of that type's numeric_limits?

< type_traits> 标头的目标似乎是将所有类型分类助手收集到一个地方，而较早的 numeric_limits 仅收集特定于，好，数字.如果不赞成使用 numeric_limits< T> :: is_integer ，则将存在一个稍微任意的边界，这些边界的类型特征存在于< type_traits> 中，并且被视为数字特征.在两个地方都拥有它并不是一个可怕的重复.

It seems to be the goal of the <type_traits> header to gather all the type classification helpers in one place, while the older numeric_limits collects only properties specific to, well, numbers. If numeric_limits<T>::is_integer were deprecated, there'd be a slightly arbitrary boundary which type traits lived in <type_traits>, and which were considered numerical. It's hardly a terrible duplication to have it in both places.

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