C ++：“断言（此）”是可行的模式吗？

Suppose the C++ below. Before calling of a->method1() it has an assert (a) to check if a is sane.

The call a->method2() has no such assertion; instead method2 itself checks for a valid this by means of assert (this).

它是可行的代码。 C ++规范？

即使标准涵盖了它，但它当然不是很好的样式，并且 如果代码更改，则容易出错，例如如果方法是 重构为虚拟方法。我只是好奇什么 标准必须说，无论是g ++代码字是通过设计还是仅通过 事故。

The code below works as expected with g++, i.e. the assertion in method2 triggers as intended, because just to call method2 no this pointer is needed.

#include <iostream>
#include <cassert>

struct A
{
    int a;
    A (int a) : a(a) {}

    void method1 ()
    {
        std::cout << a << std::endl;
    }

    void method2 ()
    {
        assert (this);
        std::cout << a << std::endl;
    }
};

void func1 (A *a)
{
    assert (a);
    a->method1();
}

void func2 (A *a)
{
    a->method2();
}

int main ()
{
    func1 (new A (1));
    func2 (new A (2));
    func2 (nullptr);
}

输出量

1
2
Assertion failed: this, file main.cpp, line 16