属性如何在面向对象的 MATLAB 中工作？
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How do properties work in Object Oriented MATLAB?
提问by
I am trying to create a MATLAB class with a member variable that's being updated as a result of a method invocation, but when I try to change the property within the class it (apperently, from what I understood from MATLAB's memory management) creates a copy of the object and then modifies it, leaving the original object's property untouched.
我正在尝试创建一个带有成员变量的 MATLAB 类，该成员变量因方法调用而更新，但是当我尝试更改类中的属性时，它（显然，根据我对 MATLAB 内存管理的理解）创建了一个副本对象，然后修改它，保持原始对象的属性不变。
classdef testprop
properties
numRequests=0;
end
methods
function Request(this, val)
disp(val);
this.numRequests=this.numRequests+1;
end
end
end
.
.
>> a=testprop;
>> a.Request(9);
>> a.Request(5);
>> a.numRequests
ans = 0
回答by Azim
Using a Vanilla Class
使用 Vanilla 类
When using vanilla class you need to tell Matlab to store a modified copy of the object to save the changes in the property value. So,
使用 vanilla 类时，您需要告诉 Matlab 存储对象的修改副本以保存属性值的更改。所以，
>> a=testprop
>> a.Request(5); % will NOT change the value of a.numRequests.
5
>> a.Request(5)
5
>> a.numRequests
ans =
0
>> a=a.Request; % However, this will work but as you it makes a copy of variable, a.
5
>> a=a.Request;
5
>> a.numRequests
ans =
2
Using the Handle Class
使用句柄类
If you inherit from the handle class, that is
如果你从handle类继承，那就是
classdef testprop < handle
then you can write,
然后你可以写，
>> a.Request(5);
>> a.Request(5);
>> a.numRequests
ans =
2
Update: Using Vanilla Class
更新：使用 Vanilla 类
As Kamrannotes for the above to work the definition of the Requestmethod in the question's example code needs to be changed to include an output argument of type testprop.
正如Kamran 所指出的，要使上述内容起作用，Request需要更改问题示例代码中方法的定义，以包含类型testprop的输出参数。
Thanks Kamran.
谢谢卡姆兰。
回答by Marc
You have to remember that syntactically in Matlab, you're probably closer to C, than C++ or Java, at least with respect to objects. So, of you want to change the "contents" of a value object (really just a special struct), you need to return the object from the function.
您必须记住，在 Matlab 中的语法上，您可能更接近 C，而不是 C++ 或 Java，至少在对象方面。所以，如果你想改变一个值对象的“内容”（真的只是一个特殊的struct），你需要从函数中返回对象。
Azim was correct to point out that if you want Singletonbehavior (which, from your code, you seem to), you need to use a "handle" class. Instances of classes that derive from Handle all point to a single instance, and operate only on it.
Azim 正确地指出，如果您想要单例行为（从您的代码来看，您似乎是这样），您需要使用“句柄”类。从 Handle 派生的类的实例都指向单个实例，并且只对它进行操作。
You can read more about the differences between Value and Handle classes.
回答by Kamran Bigdely
I made the class testpropand tried to excute the code which Azim suggested but it did not work. When I executed the following command:
我创建了类testprop并尝试执行 Azim 建议的代码，但它不起作用。当我执行以下命令时：
a=a.Request(1)
The following error was generated:
产生了以下错误：
??? Error using ==> Request Too many output arguments.
？？？错误使用 ==> 请求太多的输出参数。
I think the problem is that we did not determine any output when declaring Requestmethod. So we should change it to:
我认为问题在于我们在声明Request方法时没有确定任何输出。所以我们应该把它改成：
function this = Request(this, val)
and now:
现在：
>> a = testprop;
>> a = a.Request(1);
>> a.numRequests
ans = 1
