Retrieve an object's name

I've used Matlab a long time (10+ years) but for the life of me I can't do something rather stupidly simple: get an object's name (not its class name but the name of a specific instance). For testing purposes, I just need a function to print out the name of a specific instance of an object. Surely there is a straightforward way to do this that I'm overlooking but it doesn't easily show up in any of the help retrievals I've tried. None of my fellow Matlab users here at work could give me any help. (I know I'm going to be red-faced when I learn (relearn?) the method.)

Answer 1

[Sean de Wolski]

whos

?

x = whos;
idx = cellfun(@(x)strcmp(x,'double'),{x(:).class}); %change 'double' to your class
x(idx).name

[Christopher Ison]

Thanks for the speedy reply! Yes, this seems to work pretty well at the command prompt. I will do some more testing inside functions to see how well it works there.

[Sean de Wolski]

It works fine in functions, you may just have to wrap it with 'evalin' to go up a layer.

[Lucas Schneeberger]

I did it and I think that does not work if you have several instances of the same class

[CCC]

I would like to do that with a method within the instance itself.

If you use evalin for example in 'base' you may overwrite x if exists (can be solved)

but then you get, as Lucas mentioned a list of the same class, you could add a unique property to each instance so that:

Looking for something more elegant!

function charname = getInstanceName(obj)

% Handle this variables as inputs, properties or whatever you want:
yourclass = obj.type; % Any comand that returns your instance's class.
workspaceoftheinstance = 'base';
propertyID = 'Reference'; % Any unique ID of your instance.

% Just a way to avoid using X, looking for a better one, or
% simply use the 'else'.
if ~evalin(workspaceoftheinstance,'exist(''x'')')
    evalin(workspaceoftheinstance,'x = whos;');
    x = evalin('base','x');
else
    evalin(workspaceoftheinstance,...
        'super_long_variable_name_nobody_would_use_for_this = whos;');
    x = evalin(workspaceoftheinstance,...
        'super_long_variable_name_nobody_would_use_for_this');
end

% Same as the Accepted Answer:
idx = cellfun(@(x)strcmp(x,yourclass),{x(:).class});

instances = x(idx);

if length(instances)>1

% We try to solve the list of instances of the same class with the 
% unique .Reference property (same solution as Accepted Answer):

    for i = 1:length(instances)
        if evalin(workspaceoftheinstance,['strcmp(',instances(i).name,'.',propertyID,...
                                         ',''',obj.Reference,''')'])
            charname = instances(i).name;
            obj.varname = instances(i).name;
            break
        end
    end
else
        % There's only one.
        charname = instances.name;
        obj.varname = instances.name;
end    

end

[Steven Lord]

IF you're doing this for diagnostic purposes (to include the name of the input in a warning or error message) and not to try to reach into the calling workspace to modify the object and if you're able to handle the scenario where the input has no name use inputname.

x = 1:10;
showInputName(x)

The name of the input is 'x'.

showInputName(1:10)

The input has no name.

function showInputName(in)
s = inputname(1);
if isempty(s)
    fprintf("The input has no name.\n")
else
    fprintf("The name of the input is '%s'.\n", s)
end
end

Answer 2

[Christopher Ison]

Well, I found the short answer and it's really, really stupid:

function namestr = getobjname(obj)
namestr = inputname(1);

So if I type this at the command line:

namestring = getobjname(myobject)

If "myobject" exists, it returns

>>namestring = myobject

which can now be printed in an output display. Very helpful, Mathworks.

[tom_brot]

This is a very neat solution. I do it like this now:

methods
       function name = objName(self)
            name = inputname(1);
       end
end

In this way you get your objects Name by

yourobject.objName

The Problem is, this works perfectly from outside the object, but it doesn't works in another method.

methods
     function displayname(obj)
          display(obj.objName)
     end
end

Then the output is just

obj

So the new Task is: Retrieve an object's name WITHIN A METHOD

any ideas?

[Sean de Wolski]

This was discussed here Tom:

http://www.mathworks.com/matlabcentral/answers/130695-how-can-i-return-a-char-of-object-variable-name-from-a-method

[Lucas Schneeberger]

Is there a way to get the name of the instance inside the class constructor ? I would like to assign a value to obj.name property during the object construction.

This would require the left part of the assignment as in

instance_name = Class(varargin)

to be already processed when constructing the object, I am not sure if it is the case ...

[Steven Lord]

I would like to assign a value to obj.name property during the object construction.

See the "Initializing Objects in Constructor" section on this documentation page for several examples of how to do this. There's no need to know with what name the class constructor was called to store the output (or even if that output has a name: mycell{1} = myObjectConstructor; is a perfectly valid way to call an object constructor and store the resulting object in a cell in a cell array.)

Answer 3

[Paul O'Brien]

In MatLab R2016b, if I have a variable "obj" referring to an object, you can get a list of methods by typing

obj.

and then pressing the tab key. One of the methods is called "string", and

obj.string

yields a string containing the name of the object.

[Steven Lord]

That assumes that the class author has chosen to overload the string method to behave that way. As an example of where this could fail is the table class:

>> t = array2table(magic(4));
>> class(t)

ans =

    'table'

>> string(t)
Error using string
Conversion to string from table is not possible.

This is one case where string(t) and t.string behave differently, but neither gives the name of the variable.

>> t.string
Unrecognized variable name 'string'.