How can I add a method to a table class?

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Ronald Stahl
Ronald Stahl 2023-12-28
编辑： Sai Teja G 2024-1-5
When a class is definded using an @class folder, new methods could be added in another @class folder of the same name somewhere else in the Matlab path. is there anything equivalent in a class defined using "classdef", such as with the "table" class? Adding an @table folder in the Matlab path doesn't work.

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Sai Teja G
Sai Teja G 2023-12-28
编辑：Sai Teja G 2024-1-5
Hi Ronald,
I understand that you wish to add new methods within a separate class folder, rather than in the same MATLAB path.
You can extend the functionality of a `classdef` class in different ways:
1. Inheritance:
classdef NewClass < OriginalClass
% New methods and properties here
end
2. Method Overloading:
classdef MyTable < table
methods
function obj = MyTable(varargin)
obj@table(varargin{:});
% Constructor can be customized here
end
% Overloaded or new methods here
end
end
3. Composition:
classdef MyClass
properties
TableInstance
end
methods
function obj = MyClass(data)
obj.TableInstance = table(data);
% Additional constructor code here
end
% New methods that use obj.TableInstance here
end
end
Regarding the specific case of adding methods to the "table" class, it is a built-in class and MATLAB does not support directly adding methods to it via an "@table" folder. You would need to use one of the above methods to extend its functionality.
Hope it helps!

更多回答（2 个）

Shubham
Shubham 2023-12-28
Hi Ronald,
In MATLAB, when you define a class using the classdef keyword in a single file (not in an @class folder), the class is considered to be a "sealed" class, meaning that its definition is complete and cannot be extended by adding new methods in separate locations on the MATLAB path. This is in contrast to the old-style classes defined using @class folders, where methods could be spread across multiple @class folders on the path.
For classes defined using classdef, all methods must be included within the class file or in separate files within the same class folder (if the class is defined across multiple files). You cannot extend such a class by simply creating an @classname folder elsewhere on the path.
However, there are a few ways you can extend functionality for such classes:
  • Inheritance: Create a subclass that inherits from the classdef class and adds new methods or properties. This is the standard object-oriented way to extend functionality.
classdef MyTableSubclass < table
% Your new methods and properties here
end
  • Composition: Create a new class that contains an instance of the class you want to extend and delegate method calls to that instance.
classdef TableWrapper
properties
InternalTable table
end
methods
function obj = TableWrapper(t)
if nargin > 0
obj.InternalTable = t;
end
end
% Your new methods here, which use obj.InternalTable
end
end
  • Package Folders: While you cannot add methods to a class from outside its @class folder, you can organize classes into packages using +package folders. This won't allow you to add methods to an existing class, but you can create related functions that are grouped under a package namespace.
% Inside folder +myTablePackage
function out = myNewFunction(t)
% Function that operates on a table object
end
You would then call this function as out = myTablePackage.myNewFunction(myTableObj);
  • External Functions: Simply create functions that accept instances of the class as inputs. This is not the same as adding methods to the class itself, but it allows you to create additional functionality that operates on the class instances.
function out = myFunctionForTable(t)
% Your code that operates on the table instance 't'
end
Unfortunately, if you want to add methods to MATLAB's built-in classes (like table), you're generally limited to these approaches. You cannot modify the built-in classes directly due to how they are sealed and managed by MATLAB's internal mechanisms.
Ronald Stahl
Ronald Stahl 2023-12-28
编辑：Ronald Stahl 2023-12-28
Thanks for the detailed answer!
I had thought to add an overloaded "plot" function to the table class but I see that it's not that simple. I'll look at implementation using your ideas/suggestions.

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