一个类或者结构重载小括号运算符 使其看起来像一个函数
注意 vector里面存的是非指针 重载的小括号的参数也要是非指针 vector里存的变量类型要和小括号的参数类型一致

struct FindRv
{
    SnakeBody body;
    FindRv(SnakeBody& body) {
        this->body = body;
    }

    bool operator()(SnakeBody& sb) {
        return body == sb;
    }
};
struct FindPv
{
    SnakeBody body;
    FindPv(SnakeBody body) {
        this->body = body;
    }

    bool operator()(SnakeBody* sb) {
        return body == sb;
    }
};

int main()
{

    std::vector<SnakeBody> rv;
    std::vector<SnakeBody*> pv;

    rv.push_back(SnakeBody(1, 2, 1));
    pv.push_back(new SnakeBody(1, 1, 1));

    SnakeBody tsb(1,1,2);

    std::find_if(rv.begin(), rv.end(), FindRv(tsb));
    std::find_if(pv.begin(), pv.end(), FindPv(tsb));

}