OOP in Matlab: input arguments for methods other than constructor

When trying to modify object properties in the command window, it seems that the first input argument (the object name) is always omitted. Why is this the case?

Also, when I make the object name the second input argument, then I get the following error: "Attempt to reference field of non-structure array." Why does the object have to be the first input argument?

An example (straight from MathWorks documentation) is shown below, and the relevant line is the "withdraw" method. As you can see, the object is an input argument but when you use this method from the command window you say BA.withdraw(600) instead of BA.withdraw(BA,600). Why is that?

I took the code below from: Developing Classes — Typical Workflow

Thank you!

classdef BankAccount < handle
 properties (Hidden)
    AccountStatus = 'open'; 
 end
 % The following properties can be set only by class methods
 properties (SetAccess = private)
    AccountNumber
    AccountBalance = 0; 
 end
 % Define an event called InsufficientFunds
 events
    InsufficientFunds 
 end
 methods
    function BA = BankAccount(AccountNumber,InitialBalance)
       BA.AccountNumber = AccountNumber;
       BA.AccountBalance = InitialBalance;
       % Calling a static method requires the class name
       % addAccount registers the InsufficientFunds listener on this instance
       AccountManager.addAccount(BA);
    end
    function deposit(BA,amt)
       BA.AccountBalance = BA.AccountBalance + amt;
       if BA.AccountBalance > 0
          BA.AccountStatus = 'open';
       end
    end
    function withdraw(BA,amt)
       if (strcmp(BA.AccountStatus,'closed')&& BA.AccountBalance < 0)
          disp(['Account ',num2str(BA.AccountNumber),' has been closed.'])
          return
       end
       newbal = BA.AccountBalance - amt;
       BA.AccountBalance = newbal;
       % If a withdrawal results in a negative balance,
       % trigger the InsufficientFunds event using notify
       if newbal < 0
          notify(BA,'InsufficientFunds')
       end
    end % withdraw
 end % methods
end % classdef

Answer 1

[per isakson]

"BA.withdraw(600) instead of BA.withdraw(BA,600)."

There are two alternative ways to call a method

    withdraw( BA, 600 )

and

    BA.withdraw( 600 )

(remember BankAccount is a handle class).

"Why does the object have to be the first input argument?" &nbsp and &nbsp " Why is that?" &nbsp I have no better answer than: At The Mathworks they decided on that syntax. However, there is a function, why :-)

See Comparing MATLAB with Other OO Languages

[Pacman Pacman]

Thank you, Per. If I use the first way to call the method then it turns out that the object does not have to be the first input argument. Too bad I can't change the syntax decisions!

[per isakson]

"If I use the first way to call the method then it turns out that the object does not have to be the first input argument." &nbsp I don't understand what you mean. There are these two ways to call a method, but only one to define it

    function withdraw( BA, amt )

In the documentation they nearly always use the name obj

    function withdraw( obj, amt )

and I use

    function withdraw( this, amt )

(the syntax of static methods is different)