MATLAB: How to determine the objects base workspace variable name inside a method/function of the class in MATLAB

baseMATLABmcosoopworkspace

Is there a MATLAB function that can determine the workspace name for a given argument. Something like function who() but that would take a MATLAB object as an argument and return a string.

I have a custom classdef class that I work with frequently, and have overloaded the functions save() and load() for this class. I declared my save function as:

 function save(obj,fileName)

and typically use the workspace variable name as (fileName), so for example:

 >>myObj = MyClass; 
 >>myObj.save('myObj') 
 >>... 
 >>MyClass.load('myObj') % creates (myObj) in base workspace

Ideally, I would like to be able to determine the class object's workspace name within my overloaded save() method. So for example, I would like to be able to execute the above steps as:

 >>myObj1 = MyClass; 
 >>myObj1.save 
 >>... 
 >>MyClass.load('myObj1') % creates (myObj1) in base workspace

I realize that I could require the object name to be specified in the class constructor, but I don't like this idea; for example:

 >>myObj2 = MyClass('myObj2'); 
 >>myObj2.save 
 >>... 
 >>MyClass.load('myObj2') % creates (myObj2) in base workspace

I expected to find a Matlab function call that would determine the workspace name for a given argument. Something like function who() but that would take a Matlab object as an argument and return a string. For example,

 >>myObj3 = MyClass('myObj3'); 
 >>objectName = who(myObj3,'base') % look in base workspace 
 ans = 'myObj3'

I could then use this function call within MyClass.save() to determine the workspace name of the class object.

Best Answer

This can be done using the INPUTNAME function in MATLAB.

http://www.mathworks.com/access/helpdesk/help/techdoc/ref/inputname.html

You may access the same page locally by typing the following at the MATLAB prompt:

web([docroot,'/techdoc/ref/inputname.html'])

Related Solutions

MATLAB: How to determine all the objects of a particular class from the base workspace in MATLAB

In order to do this you can write a simple function that would evaluate all the variables in the base workspace and then compare the class to which they belong. Once you find the desired classname you can return the name of that variable as a string.

Here is the function that shows how this could be done:

function out = get_Objects_From_Base(classname)
     baseVariables = evalin('base' , 'whos')
     out = cell(0);
     for i = 1:length(baseVariables)
         if (strcmpi(baseVariables(i).class , classname)) % compare classnames
             out{length(out) +1}  = baseVariables(i).name;
         end  
     end
end

The function takes in an input class name and returns the name of ALL objects that are of that class from the base workspace. The example usage below will return a cell array containing the string 'objA1'

>> objA1 = myclassA;
>> get_Objects_From_Base('myclassA')

MATLAB: How are objects converted from one type to another when collected together in an array in MATLAB 7.6 (R2008a)

When MATLAB sees a subscripted assignment to an existing variable, MATLAB checks the class of the right-hand-side against the class of the left-hand-side (LHS) variable. If different, it attempts to convert the right-hand-side (RHS) variable to the type of the LHS class.

To achieve this, MATLAB first looks for a method of the RHS class that has the same name as the LHS class. This is a converter method from one class to another and similar in some ways to a cast operator in C++.

If there is no specific converter, then MATLAB calls the LHS constructor and passes the RHS variable as input. This is irrespective of the class relationship between the LHS and RHS variable.

In the above example, the LHS class is SuperClass and the RHS class is SubClass. When the following line is executed,

vec(2) = subobj

since SubClass does not have a method SuperClass, MATLAB calls the SuperClass constructor with subobj as the single input, resulting in an error.

To facilitate the conversion from SubClass to SuperClass, you can create a method named SuperClass in class SubClass with the following signature

function obj = SuperClass(subobj)
      obj = SuperClass(subobj.prop1, subobj.prop2);
end

Alternatively, you can modify the constructor of SuperClass to accommodate single inputs of type SuperClass. One implementation of the constructor could be,

function obj = SuperClass(prop1, prop2)
      if isa(prop1,'SuperClass')
          obj.prop1 = prop1.prop1;
          obj.prop2 = prop1.prop2;
      else
          obj.prop1 = prop1;
          obj.prop2 = prop2;
      end
end

One drawback of the previous methods is that a copy of the object is created.

As an alternative, you can preserve the original class of the objects and still aggregate the objects by using a cell array as follows:

vec{1} = supobj;
vec{2} = subobj;

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