How can I return a char of object variable name from a method

How can I return a variable that represents a string of the variable name of an object, using a method of that object?

Here is a simple example:

classdef whatsMyName < handle
    methods
        function obj = whatsMyName()
        end
        function [ out ] = myNameIs(obj)
            out = inputname(1);
            fprintf('(1)my name is %s\n', out)
        end
        function [ out ] = orMaybeMyNameIs(obj)
            out = obj.myNameIs;
            fprintf('(2)my name is %s\n', out)
        end
    end
end

>> w.myNameIs;
(1)my name is w

>> w.orMaybeMyNameIs;
(1)my name is obj
(2)my name is obj

I'd like to be able to return "w" from the call inside a method.

Answer 1

[Sean de Wolski]

Why not just store it as a property?

More

If it ONLY needs to work from one method calling _oneother methods (i.e. not method1 calling method2 asking for name), you can use evalin:

name = evalin('caller','inputname(1)')

Class:

classdef whatsMyName < handle
    methods
        function obj = whatsMyName()
        end
        function [ out ] = myNameIs(obj)
            out = evalin('caller','inputname(1)')
            fprintf('(1)my name is %s\n', out)
        end
        function [ out ] = orMaybeMyNameIs(obj)
            out = obj.myNameIs;
            fprintf('(2)my name is %s\n', out)
        end
    end
end

Example:

howdy = whatsMyName

howdy = 

    whatsMyName with no properties.

orMaybeMyNameIs(howdy)

out =

howdy

(1)my name is howdy
(2)my name is howdy

ans =

howdy

[Sean de Wolski]

Well I suppose since it's a handle class you could have multiple handles with different names so this might not work.

Why do you want a self-identifying object anyway?

[Brent Wyk]

I would ok with storing it as a property if I could set the property from inside a method of the object.

Self-identifying object is pretty easy -- the example method does that. But I would like the methods to know what the object is called in the global workspace (without having to manually set a property value in that workspace).

As to the reason, I want to be able to suggest what a user should enter on the command line. So if they call the object 'HOWDY' the help could tell them "type Howdy.world on the command line to continue"

[Sean de Wolski]

See More

[Brent Wyk]

I found another use, which is to allow an object method to save the object with proper names:

function sav(obj)
          s = obj.myNameIs;
          eval([s ' = obj;']);
          save(s, s);
end

[Sean de Wolski]

Or you could just overload saveobj which will be cleaner and not require evil.

http://www.mathworks.com/help/releases/R2014a/matlab/ref/saveobj.html

[Cedric]

While this was not part of the question, I should add that this works because

 howdy.myNameIs()

is equivalent to

 myNameIs(howdy)

and howdy is hence the variable name of the first input. This will fail if howdy is e.g. a field or a property name:

 S.howdy = whatsMyName ;
 S.howdy.myNameIs() ;

yields

 (1)my name is 
 ans =
    0×0 empty char array

because in myNameId(S.howdy), input 1 S.howdy is not a variable name (for INPUTNAME).

This implies that an object saved as a property of another object cannot know its "property name" (at least through this means).

PS: Sean, if you knew a way for an object to know its name as a property of another object, I could use it.

[Philip Borghesani]

One more addendum to this answer:

out = evalin('caller','inputname(1)')

will not work in MATLAB R2015b or later versions of MATLAB due to a change in inputname. Inputname no longer respects the context of evalin statements or code directly called by one.

Answer 2

[Geoff Hayes]

The following method (once added to your above class) seems to do what I think you want:

function [nm] = getMyName(~)
    nm = inputname(1);
end

Just clear all and try again:

>> obj1 = whatsMyName;
>> obj1.getMyName
   obj1
>> longerName = whatsMyName;
>> longerName.getMyName
   longerName

Answer 3

[Anna Marcellan]

How is it then possible to solve this same problem with MatlabR2019b?

[Cedric]

You should redesign your approach so you don't have to rely on the object variable name.

Assuming that you can access that name, what happens if a user of your class does the following, for example:

myObjects{5} = MyClass() ;

If the name contains relevant information, this information could be passed to the constructor as a string/char array and saved in a property:

temp = MyClass('temperature');
speed = MyClass('speed');

If you absolutely need to get the variable name, you should create a new thread and refer to this one.