Question

我在一个名为Selene的项目（C ++ 11 Lua包装器）中看到过这种情况，我正在徘徊它的作用吗？

using Fun = std::function<void()>;
using PFun = std::function<void(Fun)>;

它是类（Selector）的私有成员。

周围代码：

namespace sel {
class State;
class Selector {
private:
    friend class State;
    State &_state;
    using Fun = std::function<void()>;
    using PFun = std::function<void(Fun)>;

    // Traverses the structure up to this element
    Fun _traverse;
    // Pushes this element to the stack
    Fun _get;
    // Sets this element from a function that pushes a value to the
    // stack.
    PFun _put;

    // Functor is stored when the () operator is invoked. The argument
    // is used to indicate how many return values are expected
    using Functor = std::function<void(int)>;
    mutable std::unique_ptr<Functor> _functor;

    Selector(State &s, Fun traverse, Fun get, PFun put)
        : _state(s), _traverse(traverse),
          _get(get), _put(put), _functor{nullptr} {}

    Selector(State &s, const char *name);

Answer 1

这是一种涵盖typedef功能（and more）的C ++ 11语法。在这种情况下，它会生成一个名为Fun的别名，它与std::function<void()>的类型相同：

using Fun = std::function<void()>; // same as typedef std::function<void()> Fun

这意味着你可以这样做：

void foo() 
{
  std::cout << "foo\n";
}

Fun f = foo; // instead of std::function<void()> f = foo;
f();

同样适用于PFun。

C ++这行代码是什么意思？

1 个答案: