boost-preprocessor - 升压-pp : how to determine if a macro parameter is a tuple

Question

元组是由括号括起来的逗号分隔列表，例如

()
(,)
(thing,)
(2,3)

如果我有

#define ISTUPLE(x) \\...

我想要类似 ISTUPLE(nope) 的东西解析为 0 和 ISTUPLE((yep))解决为 1。

[FWIW，我有_RTFM_'d很多。]

Answer 1

它可能会在预处理库中完成一些工作，但可变宏数据库(自发布此问题后添加到 Boost)有一个现成的解决方案。 BOOST_VMD_IS_TUPLE ，在 boost/vmd/is_tuple.hpp 中定义，应该做你正在寻找的:

#include <iostream>

#include <boost/vmd/is_tuple.hpp>

#if BOOST_VMD_IS_TUPLE() != 0
  #error BOOST_VMD_IS_TUPLE() != 0
#endif

#if BOOST_VMD_IS_TUPLE(nope) != 0
  #error BOOST_VMD_IS_TUPLE(nope) != 0
#endif

#if BOOST_VMD_IS_TUPLE((yep)) != 1
  #error BOOST_VMD_IS_TUPLE((yep)) != 1
#endif

#if BOOST_VMD_IS_TUPLE(()) != 1
  #error BOOST_VMD_IS_TUPLE(()) != 1
#endif

#if BOOST_VMD_IS_TUPLE((,)) != 1
  #error BOOST_VMD_IS_TUPLE((,)) != 1
#endif

#if BOOST_VMD_IS_TUPLE((thing,)) != 1
  #error BOOST_VMD_IS_TUPLE((thing,)) != 1
#endif

#if BOOST_VMD_IS_TUPLE((2,3)) != 1
  #error BOOST_VMD_IS_TUPLE((2,3)) != 1
#endif

static_assert(BOOST_VMD_IS_TUPLE() == 0,"BOOST_VMD_IS_TUPLE() != 0");
static_assert(BOOST_VMD_IS_TUPLE(nope) == 0,"BOOST_VMD_IS_TUPLE(nope) != 0");
static_assert(BOOST_VMD_IS_TUPLE((yep)) == 1,"BOOST_VMD_IS_TUPLE((yep)) != 1");
static_assert(BOOST_VMD_IS_TUPLE(()) == 1,"BOOST_VMD_IS_TUPLE(()) != 1");
static_assert(BOOST_VMD_IS_TUPLE((,)) == 1,"BOOST_VMD_IS_TUPLE((,)) != 1");
static_assert(BOOST_VMD_IS_TUPLE((thing,)) == 1,"BOOST_VMD_IS_TUPLE((thing,)) != 1");
static_assert(BOOST_VMD_IS_TUPLE((2,3)) == 1,"BOOST_VMD_IS_TUPLE((2,3)) != 1");

int main(void)
{
    using std::cout;
    using std::endl;
    cout << "BOOST_VMD_IS_TUPLE() == " << BOOST_VMD_IS_TUPLE() << endl;
    cout << "BOOST_VMD_IS_TUPLE(nope) == " << BOOST_VMD_IS_TUPLE(nope) << endl;
    cout << "BOOST_VMD_IS_TUPLE((yep)) == " << BOOST_VMD_IS_TUPLE((yep)) << endl;
    cout << "BOOST_VMD_IS_TUPLE(()) == " << BOOST_VMD_IS_TUPLE(()) << endl;
    cout << "BOOST_VMD_IS_TUPLE((,)) == " << BOOST_VMD_IS_TUPLE((,)) << endl;
    cout << "BOOST_VMD_IS_TUPLE((thing,)) == " << BOOST_VMD_IS_TUPLE((thing,)) << endl;
    cout << "BOOST_VMD_IS_TUPLE((2,3)) == " << BOOST_VMD_IS_TUPLE((2,3)) << endl;

    return 0;
}

输出:

BOOST_VMD_IS_TUPLE() == 0
BOOST_VMD_IS_TUPLE(nope) == 0
BOOST_VMD_IS_TUPLE((yep)) == 1
BOOST_VMD_IS_TUPLE(()) == 1
BOOST_VMD_IS_TUPLE((,)) == 1
BOOST_VMD_IS_TUPLE((thing,)) == 1
BOOST_VMD_IS_TUPLE((2,3)) == 1

( http://coliru.stacked-crooked.com/a/6e41eaf17437c5d5 )