在父级之前初始化子级-不要调用父级构造函数 [英] Initialize child before parent - do not call parent contructor

问题描述

在MatLab中，我有一个超类A，它带有一些参数x和y

In MatLab, i have a superclass A that takes some parameters, x and y

classdef A < handle
properties
   x;
   y;
   z;
end
methods
   function this = A(x, y)
      this.x = x;
      this.y = y;
      this.initialize();
   end
   function initialize(this)
      this.z = this.x + this.y;
   end
end
end

应该使用initialize方法进行一些初始计算，以便稍后进行计算.

The initialize method is supposed to do some initial calculations to fasten computation later.

现在，我想创建A的子类B，它具有自己的初始化，但是B应该在A之前初始化.

Now i want to create a child class B of A, with it's own inialization, but B should be initialized before A.

classdef B < A
properties
   p
end
methods
   % B takes another parameter p
   function this = B(p)
      % Since B is a subclass of A, and A takes some parameters we have to 
      % call the constructer of A as the first thing.
      this = this@A([], []);
      this.p = p;
   end
   function initialize(this)
      this.x = this.p(1);
      this.y = this.p(2);
      % This is when initialize of A should be called.
   end
end
end

基本上，我只想在A之前初始化B，但是由于必须首先调用父级的构造函数，所以我不知道该怎么做.

Basically i just want to initialize B before A, but because the constructer of the parent have to be called as the first thing, i cannot figure out how to do this.

在PHP中，我会做类似的事情

In PHP I would do something like this

class A {
   public function __construct($x, $y) {
      $this->x = $x;
      $this->y = $y;
      $this->initialize();
   }
   public function initialize() {
      $this->z = $this->x + $this->y;
   }
}
class B extends A {
   public function __construct($p) {
      // Does not call the parent constructor.
      $this->p = $p;
      $this->initialize();
   }
   public function initialize() {
      $this->x = $this->p[0];
      $this->y = $this->p[1];
      parent::initialize(); // Now we are ready to initialize A
   }
}

是否有一种聪明的方法来设计MatLab中我想要的东西?我必须放弃B类中A的继承吗?

Is there a smart way to design what i want in MatLab? Do i have to give up the inheritance of A in class B?

推荐答案

这违反了OOP的原理.您基本上想要实现的目标排除了B应该从A派生的情况.据我所知，您确实想重载A的构造函数.可以使用nargin签入A来执行此操作，或者如果您出于某种原因确实想要B，则只需在B的构造函数中使用:this = this@A(p(1), p(2);即可正确地调用B的构造函数A(并删除属性p).

This goes against the principles of OOP. What you are trying to achieve basically rules out that B should be derived from A. From what I can tell, you really want to overload the constructor of A. Either do this using a nargin check in A, or if you really want to have a B for whatever reason, just use: this = this@A(p(1), p(2); in the constructor of B instead, to properly call the constructor of A (and get rid of the property p).

这是您使用nargin模拟到重载构造函数的方式:

This is how you would simulate to overload the constructor by using nargin:

classdef A < handle
    properties
        x;
        y;
        z;
    end
    methods
        function this = A(x, y)
            if nargin==1 % 'p' was passed as 'x'
                this.x = x(1);
                this.y = x(2);
            else
                this.x = x;
                this.y = y;
            end
            this.initialize();
        end

        function initialize(this)
            this.z = this.x + this.y;
        end
    end
end

这是从A派生B的方法，并正确调用了A的构造函数:

This is how you would derive B from A, with a proper call of A's constructor:

classdef B < A
    methods
        function this = B(p)
            this = this@A(p(1), p(2));
        end
    end
end

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