Find instances in workspace by their properties

I have several instances of different classes in workspace, and I want to first get the instances instantiated from one class and then find the instances that have the same string property, I tried to add following method in class, but it doesn't return anything.

Or is there any easier way to find variables and get specific property values in workspace in this case? Thanks in advance.

function [ val ] = getInstance()
w = whos();
idx = strcmp({w.class}, 'xxx'); % index of instances of the same class in workspace
n = w(idx);
for k = 1 : size(n, 1)
    f = evalin('base', n(k, 1).name); % iterate through those instances 
    if strcmp(f.propertyName1, 'yyy') % find the instances of specific property string value
          t.(f.propertyName2) = f.propertyName3; % get property value and store in a struct
       else
    end
val = t;
end

[per isakson]

Shouldn't

    w = whos();

read

    w = evalin( 'base', 'whos()' );

?