与C ++中的Lua表操作最接近的是什么？

Question

最近让C ++和SDL2进行编译，并开始四处乱搞。我已经非常了解Lua和JavaScript，并且可以毫无问题地完成大多数我需要做的事情。

我希望创建一个对象，该对象可以实现类似Lua的示例，但是使用C ++。我无法在线上找到任何东西，但是我可能没有使用正确的搜索词，因为我是C ++的新手（尽管我有一定的C经验）。

foo = {
    a = 0,
    b = "hello"
    c = "world"
}

function foo:bar(baz)
    self.a = self.a + 1
    print(self.b.." "..self.c)
    table.insert(self, baz)
end

非常感谢您的帮助！

Answer 1

从a good book开始学习C ++较容易，而不是立即尝试自己玩C ++。 C ++不像Lua那样容错。

仍然，这是一些类似于您的Lua示例的C ++代码：

// Makes the standard type std::string available:
#include <string>

// Every variable needs a type.
// "class" creates a new type with given members, so here's how we'll define
// a type for variable "foo".
// A class definition like this usually goes in a header file.
class FooType
{
  public:
    // These members have default initializers, which will be used when
    // a FooType object is created without its own initializer.
    int a = 0;
    std::string b = "hello";
    std::string c = "world";

    // This declares a class member function named bar, returning nothing:
    void bar();
};

// The actual variable foo:
FooType foo;

// Defining the member function called FooType::bar :
// This might go in a source file which begins with an #include of
// the corresponding header file.
#include <iostream> // to get std::cout and std::endl
void FooType::bar()
{
    // self.a = self.a + 1 :
    // The C++ keyword "this" is similar to Lua's "self", but is a pointer.
    // All of these are equivalent:
    // (*this).a = (*this).a + 1;
    // this->a = this->a + 1;
    // a = a + 1;  // C++ automatically adds an implicit "this->" when you
                   // just name a member.
    // ++a; // A shortcut for adding one to a number.
    ++a;

    // print(self.b.." "..self.c) :
    std::cout << b << " " << c << std::endl;
    // Lua's print automatically adds a newline after its data, but
    // C++ std::cout does not. The std::endl adds a newline and then
    // "flushes" the output, making sure it gets sent out more or less
    // immediately instead of waiting for more data as an optimization.

    // table.insert(self, baz) :
    // Not possible - C++ does not allow adding members to a class which
    // aren't declared in the class definition. If you really need something
    // similar, you could use a map with name as the key, but then you would
    // need to access all those "members" via that map, not with a plain
    // obj.name expression.
}

一些注意事项：

在Lua中，冒号方法语法只是一个快捷方式。也就是说，foo:bar(t)与foo.bar(foo, t)完全相同，但是Lua会让您做类似foo.bar(0, t)的奇怪事情，这意味着self变量变为0。 （这当然可能违反bar方法的隐含约定！）在C ++中，编译器通常会实现成员函数，就好像它们是具有this附加参数的普通函数一样，但是就语言而言，成员函数与非成员函数完全不同，并且调用它的唯一方法都涉及正确类型的对象成为*this。

相关，Lua让您重新分配self，但C ++不允许您更改指针this。

Lua用“引用语义”对待表，但是在C ++中，默认值是所有变量都使用“值语义”。

-- Lua:
foo2 = foo     -- Another name for the same table.
foo2.a = 3     -- foo.a is now 3.

// C++ (within a function):
FooType foo2 = foo;  // A different independent object.
foo2.a = 3;          // foo2.a is 3, but foo.a is unchanged

FooType& foo3 = foo; // Another name for object foo.
foo3.a = 4;          // foo.a is now 4.