Can I custum "for" loop for my class instance?

Suppose I defined a class "MyClass", how can I implement an iterator for it? For example, if I write MyClass similiar to containers.Map, how can I implement my class so that following code is legal?

``` matlab
  for [key, val] = myClassObj
      do something;
  end
```

In c++, if methods "begin", "end" have been defined, then I can write something like this

``` cpp
  for (auto & element : obj) {
      dosomething();
  }
```

Similarly, for python, defining "__iter__" and "next/__next__" makes following code possible

``` python
  for element in obj:
      dosomething()
```

Is there a way to do so for "MyClass" in matlab? Matlab's "for" loop is just a range-based loop, so I think matlab should allow me to use similar syntax for "MyClass".

[Adam]

Code that tries to declare two variables on the line of a for statement is not going to be valid syntax under any circumstance, whether using a class or any other function that does this.

e.g.

for [a, b] = max( rand(7) )

gives a syntax error.

If you give more information on what you are trying to do rather than trying to enforce a syntax that simply doesn't work then we can provide more help, but trying to crowbar in desired syntax just isn't going to work.

[Qixiang Zou]

just return key is also ok,..

for key = myObj
    do something;
end

I just want to know, how to overload the for loop for my class.

Answer 1

[Jan]

No, this is not valid Matlab syntax:

for [key, val] = myClassObj
    do something;
end

The for command is defined for vector only, but accepts arrays also. The argument is evaluated when the for command is reached the first time. You code would look like this:

keySet = keys(myClassObj);
for k = 1:myClassObj.Count
  key   = keySet{k};
  value = values(myClassObj, key);
  do something;
end

I do not know a nicer method. But this might be useful: https://www.mathworks.com/matlabcentral/fileexchange/28630-foreach-for-containers-map

See also: https://www.mathworks.com/matlabcentral/answers/307290-how-can-i-iterate-over-the-keys-and-elements-in-a-containers-map