c++ - 关于逻辑运算的 Boost tribool 问题

Question

最近，我使用了 boost::logic::tribool，但有些东西对我来说很奇怪。

#include <iostream>
#include "boost/logic/tribool.hpp"


int main()
{
    boost::logic::tribool test = true && boost::logic::indeterminate;

    if(test)
    {
     std::cout << "Executes?" << std::endl;
    }

    if (true && boost::logic::indeterminate)
    {
      std::cout << "Executes 2" << std::endl;
    }

}

打印 Executes 和 Executes 2。为什么这些条件成立？我完全确定与 (indeterminate state, true) 的 AND 操作返回不确定状态？

引自 boost.org 关于 if 中的 bool 上下文

“如果三态 bool 为真则返回真，否则返回假”

编辑:评论后我添加了这个。这是我读过的最不直观的代码。

#include <iostream>
#include "boost/logic/tribool.hpp"


int main()
{
    boost::logic::tribool test = boost::logic::tribool(true) && boost::logic::indeterminate;

    if(test)
    {
     std::cout << "This will NOT execute" << std::endl;
    }

    boost::logic::tribool second = true && boost::logic::indeterminate;

    if (second)
    {
      std::cout << "This will execute" << std::endl;
    }

}

EDIT2:我需要纠正自己......谁能解释一下？

#include <iostream>
#include "boost/logic/tribool.hpp"

boost::logic::tribool LOL( )
{
   return    boost::logic::indeterminate;
}

int main()
{

 boost::logic::tribool LOL_RESULT = LOL();

    if (boost::logic::indeterminate)
    {
        std::cout << "IT WILL BE EXECUTED" << std::endl;
    }

    if (LOL_RESULT)
    {
      std::cout << "IT WILL NOT BE EXECUTED"   << std::endl;
    }
}

Answer 1

TEST(junk, tribool)
{
    auto v = boost::logic::indeterminate;
    GTEST_MESSAGE() << typeid(v).name();
}

结果:

[----------] 1 test from junk
[ RUN      ] junk.tribool
[   NOTE   ] bool (__cdecl*)(class boost::logic::tribool,struct boost::logic::detail::indeterminate_t)

boost::logic::indeterminate 是一个函数。所以它评估为真。

TEST(junk, tribool)
{
    boost::logic::tribool test = true && boost::logic::tribool{ boost::logic::indeterminate_keyword_t() };

    if (test)
    {
        GTEST_MESSAGE() << "Executes?" << std::endl;
    }

    if (true && boost::logic::tribool{ boost::logic::indeterminate_keyword_t() })
    {
        GTEST_MESSAGE() << "Executes 2" << std::endl;
    }
}

结果:

[----------] 1 test from junk
[ RUN      ] junk.tribool
[       OK ] junk.tribool (64970 ms)
[----------] 1 test from junk (68580 ms total)