I need some help for using varargin to assign properties in handle class.
Instead of using handle class, if I create a function with varargin, it works.
function out = testFunction(varargin)
% default values
startDate = '2011-11-01';
endDate = datestr(now,'yyyy-mm-dd');
% Map of parameter names to variable names
params_to_variables = containers.Map({'StartDate','EndDate'}, {'startDate','endDate'});
v = 1;
while v <= numel(varargin)
param_name = varargin{v};
if isKey(params_to_variables,param_name)
assert(v+1<=numel(varargin));
v = v+1;
% Trick: use feval on anonymous function to use assignin to this workspace
feval(#()assignin('caller',params_to_variables(param_name),varargin{v}));
else
error('Unsupported parameter: %s',varargin{v});
end
v=v+1;
end
end
But my current task is to create a super-class with many properties. There are various types of sub-classes. Different sub-class may need to use different properties. So when I create an instance of a super-class or sub-class, I need the input to be very flexible. As the example above, one sub-class only need the property 'startDate', and the other sub-class only need the property 'endDate'. Here is my code.
classdef superclass < handle
properties
startDate
endDate
end
methods
function obj = superclass(varargin)
% Map of parameter names to variable names
params_to_variables = containers.Map({'StartDate','EndDate'}, {'startDate','endDate'});
v = 1;
while v <= numel(varargin)
param_name = varargin{v};
if isKey(params_to_variables,param_name)
assert(v+1<=numel(varargin));
v = v+1;
feval(#()assignin('caller',params_to_variables(param_name),varargin{v}));
else
error('Unsupported parameter: %s',varargin{v});
end
v=v+1;
end
end
end
end
Basically I just copy and paste, it doesn't work.
So I change
feval(#()assignin('caller',params_to_variables(param_name),varargin{v}));
to
feval(#()assignin('caller',strcat('obj.',params_to_variables(param_name),varargin{v}));
or
feval(#()assignin('base',strcat('obj.',params_to_variables(param_name),varargin{v}));
or
evalin('caller',...
strcat('obj.',params_to_variables(param_name),'=',num2str(varargin{v})));
or
evalin('base',...
strcat('obj.',params_to_variables(param_name),'=',num2str(varargin{v})));
None of them works. If anyone can tell me how to solve this problem or provide me an alternative way, I appreciate it. Thank you.
Related
I like the OO programming style that matlabs App Designer uses (or at least the way I'm using it). Now I'm wondering if I can use the same style in my "normal" matlab class.
What I have now:
classdef myClass
properties
myVar;
end
methods
function Main(obj)
obj.myVar = "a";
obj = DoSomething(obj);
disp(obj.myVar) % outputs "c"
end
function obj = DoSomething(obj)
if(obj.myVar == "a")
obj.myVar="c";
else
obj.myVar = "b";
end
end
end
end
Which can be called externally using:
myClassInst = myClass;
myClassInst.Main()
I would like to get rid of all the "obj = " in the classdef, as is possible in App Designer. So something that would look like this:
classdef myClass
properties
myVar;
end
methods
function Main(obj)
obj.myVar = "a";
DoSomething(obj); % Just call the function without "obj = "
disp(obj.myVar) % outputs "a" because I didn't overwrite obj
end
function DoSomething(obj)
if(obj.myVar == "a")
obj.myVar="c";
else
obj.myVar = "b";
end
end
end
end
The equivalent of this seems to work in App Designer. So it appears you can modify variables in a class (instance?) in App Designer, while also being able to access the modified variable without explicitly overwriting your old class instance.
I noticed App Designer has all methods an properties set to (Access = private), though I'm not sure that has anything to do with it. Of course if I set everything to private, then I can't access the Main() method from outside anymore.
So my question is, how can I program in "normal" matlab, the same way as is possible in App Designer?
EDIT:
The following works in App Designer (I left out the methods/properties for the GUI elements):
classdef tmp < matlab.apps.AppBase
properties (Access = private)
myVar; % Description
end
methods (Access = private)
function doSomething(app)
if app.myVar == "a"
app.myVar = "c";
else
app.myVar = "b";
end
end
end
% Callbacks that handle component events
methods (Access = private)
% Code that executes after component creation
function startupFcn(app)
app.myVar = "a";
doSomething(app);
disp(app.myVar); % outputs "c"
end
end
end
You definitely can! All you have to do is inherit from the handle class, as opposed to a value class which is the default for matlab. You can also define private and public methods as in other languages.
The only thing you have to do is:
classdef myclass < handle % this is how you inherit from base class
properties
public_property
end
properties (Access=private)
private_property
end
methods
function obj = myclass() % class constructor
...
end
function public_function()
...
end
end
methods (Access=private)
function private_function()
...
end
end
end
Now every time you pass an object of this class to a function, you are not passing it by value, you are passing by reference (as you might be used to from python) and modifying it's properties modifies them also in the original object.
You need to inherit (< at the top of the class) from a handle class
classdef myClass < handle
properties
var
end
methods
function obj = myClass( varargin )
% Constructor function, called automatically when object is created
end
function someFunction( obj )
obj.randomizeVar(); % Equivalent to randomizeVar( obj );
end
function randomizeVar( obj )
obj.var = rand();
end
end
end
See the documentation for the difference between a "handle" and "value" class:
A value class constructor returns an object that is associated with the variable to which it is assigned. If you reassign this variable, MATLAB® creates an independent copy of the original object. If you pass this variable to a function to modify it, the function must return the modified object as an output argument. For information on value-class behavior, see Avoid Unnecessary Copies of Data.
A handle class constructor returns a handle object that is a reference to the object created. You can assign the handle object to multiple variables or pass it to functions without causing MATLAB to make a copy of the original object. A function that modifies a handle object passed as an input argument does not need to return the object.
Moreover, if you edit matlab.apps.AppBase, the class which you app designer code inherits, you can see that the first line is
classdef AppBase < handle
So you are literally doing the same thing, without the AppBase middle-man.
In Matlab, I can define a class as such:
classdef klass < handle
properties(Dependent)
prop
end
end
Matlab is perfectly happy instantiating an object of this class, even without defining a getter for prop. It only fails when I try to access it (understandably). I'd like to set the GetMethod dynamically based upon the property's name.
Unfortunately, even when the property is Dependent, the meta.property field for GetMethod is still read-only. And while inheriting from dynamicprops could allow adding a property and programmatically setting its GetMethod in every instance, I don't believe it could be used to change an existing property. I may have to go this route, but as prop must exist for every object I'd prefer to simply set the getter on a class-by-class basis. Is such a thing possible?
An alternative solution could be through some sort of catch-all method. In other languages, this could be accomplished through a Ruby-like method_missing or a PHP-like __get(). But as far as I know there's no (documented or otherwise) analog in Matlab.
(My use case: this class gets inherited by many user-defined subclasses, and all their dependent properties are accessed in a similar way, only changing based on the property name. Instead of asking users to write get.* methods wrapping a call to the common code for each and every one of their dependent properties, I'd like to set them all dynamically with anonymous function pointers containing the necessary metadata).
Here is my proposal: create a method in the superclass called add_dyn_prop. This method is to be called in the subclasses instead of creating a dependent property the usual way.
The idea is that the superclass inherit from dynamicprops and use addprop to add a new property, and set its accessor methods manually based on its name.
classdef klass < dynamicprops
methods (Access = protected)
function add_dyn_prop(obj, prop, init_val, isReadOnly)
% input arguments
narginchk(2,4);
if nargin < 3, init_val = []; end
if nargin < 4, isReadOnly = true; end
% create dynamic property
p = addprop(obj, prop);
% set initial value if present
obj.(prop) = init_val;
% define property accessor methods
% NOTE: this has to be a simple function_handle (#fun), not
% an anonymous function (#()..) to avoid infinite recursion
p.GetMethod = #get_method;
p.SetMethod = #set_method;
% nested getter/setter functions with closure
function set_method(obj, val)
if isReadOnly
ME = MException('MATLAB:class:SetProhibited', sprintf(...
'You cannot set the read-only property ''%s'' of %s', ...
prop, class(obj)));
throwAsCaller(ME);
end
obj.(prop) = val;
end
function val = get_method(obj)
val = obj.(prop);
end
end
end
end
now in the subclass, instead of defining a dependent property the usual way, we use this new inherited function in the constructor to define a dynamic property:
classdef subklass < klass
%properties (Dependent, SetAccess = private)
% name
%end
%methods
% function val = get.name(obj)
% val = 'Amro';
% end
%end
methods
function obj = subklass()
% call superclass constructor
obj = obj#klass();
% define new properties
add_dyn_prop(obj, 'name', 'Amro');
add_dyn_prop(obj, 'age', [], false)
end
end
end
The output:
>> o = subklass
o =
subklass with properties:
age: []
name: 'Amro'
>> o.age = 10
o =
subklass with properties:
age: 10
name: 'Amro'
>> o.name = 'xxx'
You cannot set the read-only property 'name' of subklass.
Of course now you can customize the getter method based on the property name as you initially intended.
EDIT:
Based on the comments, please find below a slight variation of the same technique discussed above.
The idea is to require the subclass to create a property (defined as abstract in the superclass) containing the names of the desired dynamic properties to be created. The constructor of the superclass would then create the specified dynamic properties, setting their accessor methods to generic functions (which could customize their behavior based on the property name as you requested). I am reusing the same add_dyn_prop function I mentioned before.
In the subclass, we are simply required to implement the inherited abstract dynamic_props property, initialized with a list of names (or {} if you dont want to create any dynamic property). For example we write:
classdef subklass < klass
properties (Access = protected)
dynamic_props = {'name', 'age'}
end
methods
function obj = subklass()
obj = obj#klass();
end
end
end
The superclass is similar to what we had before before, only now is it its responsibility to call the add_dyn_prop in its constructor for each of the property names:
classdef klass < dynamicprops % ConstructOnLoad
properties (Abstract, Access = protected)
dynamic_props
end
methods
function obj = klass()
assert(iscellstr(obj.dynamic_props), ...
'"dynamic_props" must be a cell array of strings.');
for i=1:numel(obj.dynamic_props)
obj.add_dyn_prop(obj.dynamic_props{i}, [], false);
end
end
end
methods (Access = private)
function add_dyn_prop(obj, prop, init_val, isReadOnly)
% input arguments
narginchk(2,4);
if nargin < 3, init_val = []; end
if nargin < 4, isReadOnly = true; end
% create dynamic property
p = addprop(obj, prop);
%p.Transient = true;
% set initial value if present
obj.(prop) = init_val;
% define property accessor methods
p.GetMethod = #get_method;
p.SetMethod = #set_method;
% nested getter/setter functions with closure
function set_method(obj,val)
if isReadOnly
ME = MException('MATLAB:class:SetProhibited', sprintf(...
'You cannot set the read-only property ''%s'' of %s', ...
prop, class(obj)));
throwAsCaller(ME);
end
obj.(prop) = val;
end
function val = get_method(obj)
val = obj.(prop);
end
end
end
end
Note: I did not use ConstructOnLoad class attribute or Transient property attribute, as I am still not sure how they would affect loading the object from a saved MAT-file in regards to dynamic properties.
>> o = subklass
o =
subklass with properties:
age: []
name: []
>> o.name = 'Amro'; o.age = 99
o =
subklass with properties:
age: 99
name: 'Amro'
Check if this is what you want. The problem is that the user will need to get the properties using (), which may be quite boring, but anyway, I think this way you can change the variables. You can't change them directly on the class, but you can change the objects property values on demand. It doesn't need to change the values on the constructor, you can do that using another function that will be inherited by the classes.
klass1.m
classdef(InferiorClasses = {?klass2}) klass < handle
methods
function self = klass
selfMeta = metaclass(self);
names = {selfMeta.PropertyList.Name};
for name = names
switch name{1}
case 'prop_child_1'
self.(name{1}) = #newGetChild1PropFcn;
case 'prop_child_2'
self.(name{1}) = #newGetChild2PropFcn;
end
end
end
end
methods(Static)
function out = prop
out = #defaultGetPropFcn;
end
end
end
function out = defaultGetPropFcn
out = 'defaultGetPropFcn';
end
function out = newGetChild1PropFcn
out = 'newGetChild1PropFcn';
end
function out = newGetChild2PropFcn
out = 'newGetChild2PropFcn';
end
klass2.m
classdef klass2 < klass
properties
prop_child_1 = #defaultGetChildPropFcn1
prop_child_2 = #defaultGetChildPropFcn2
end
methods
function self = klass2
self = self#klass;
end
end
end
function out = defaultGetChildPropFcn1
out = 'defaultGetChildPropFcn1';
end
function out = defaultGetChildPropFcn2
out = 'defaultGetChildPropFcn2';
end
Output:
a = klass2
b=a.prop_child_1()
b =
newGetChild1PropFcn
Just started crash coursing in Matlab OO programing and I would like to write a set method for a object that will set the value then reciprocate by setting itself in the relevant field on the other object.
classdef Person
properties
age;
sex;
priority; % net priority based on all adjustment values
adjustment; % personal adjustment value for each interest
family;
end
methods
function obj = set.sex(obj, value)
if value == 'm' || value == 'f'
obj.sex = value;
else
error('Sex must be m or f')
end
end
function obj = set.family(obj,value)
if class(value) == 'Family'
obj.family = value;
else
error('Family must be of type Family')
end
end
end
end
classdef Family
properties
husband;
wife;
children;
elders;
adjustment; % interest adjustment values
end
methods
function this = set.husband(this,person)
if class(person) == 'Person'
this.husband = person;
person.family = this;
else
error('Husband must be of type Person')
end
end
function this = set.wife(this,person)
if class(person) == 'Person'
this.wife = person;
person.family = this;
else
error('Wife must be of type Person')
end
end
end
end
So what I have to do now is:
p = Person
f = Family
f.husband = p
p.family = f
What I would like is for family and person to auto set themselves in each other:
p = Person
f = Family
f.husband = p
And Family set.husband function will set p's family value to f. Why is my code not working? As far as I can tell I'm doing what is suggested in the comments.
Edit:
After some messing around I've confirmed that "this" and "person" are objects of the correct type. Ultimately the issue is that Matlab passes by value rather then by reference. Unless anyone knows a way around that I'll answer myself when I can.
Normal objects are usually considered value objects. When they are passed to a function or a method, only the value is passed not a reference to the original object. Matlab may use a read-only referencing mechanism to speed things up, but the function or method cannot change the properties of the original object.
To be able to pass an input parameter by reference, your custom object needs to be a handle object. Simply when defining your class, inherit from handle and that should do the trick:
classdef Person < handle
and
classdef Family < handle
I am trying to create a Matlab Class, where the methods attributes are changed in the Class Constructor. The purpose of this is to hide / make visible some methods, depending on the class input.
For example:
classdef (HandleCompatible) myClass < dynamicprops & handle % & hgsetget
properties (Hidden)
myProp
end
methods (Hidden)
function obj = myClass(input)
%class constructor
%add some dynamic properties
switch input
case 1
%unknown code:
%make myMethod1 visible
case 2
%unknown code:
%make myMethod2 visible
otherwise
%unknown code:
%make myMethod1 visible
%make myMethod2 visible
end
end
end
methods (Hidden)
function myMethod1 (obj, input)
%function...
end
function output = myMethod2(obj, input)
%function...
end
end
end
I tried to use the following:
mco = metaclass(obj);
mlist = mco.MethodList;
mlist(myMethod1Index).Hidden = false;
, but I get the following error:
Setting the 'Hidden' property of the 'meta.method' class is not allowed.
Thank you for your reply.
This could be a solution, if I need to access my methods selectively in the class constructor. Though, I need to use these methods in my program, and to have them visible or not, at tab completion:
%Obj1
myObj1 = myClass (inputs, '-1');
myObj1.myMethod1(arg);
%myObj1.myMethod2 - hidden
%Obj2
myObj2 = myClass (inputs, '1');
%myObj2.myMethod1 - hidden
value1 = myObj2.myMethod2(arg);
%Obj3
myObj3 = myClass (inputs, '0');
myObj3.myMethod1(arg);
value2 = myObj3.myMethod2(arg);
%here i want to be able to access both methods
Maybe it is possible to select the method properties, during class constructor, and change the attributes. But this has to be done without using the metaclass
Why not expose only a factory method and build instances of different classes depending on the input? You can use access qualifiers to lock things down like so:
% a.m
classdef a
properties, a_thing, end
methods ( Access = ?factory )
function obj = a()
end
end
end
% b.m
classdef b
properties, b_thing, end
methods ( Access = ?factory )
function obj = b()
end
end
end
% factory.m
classdef factory
methods ( Static )
function val = build(arg)
if isequal(arg, 'a')
val = a;
else
val = b;
end
end
end
end
Is there a better way to implement copy construcor for matlab for a handle derived class other than adding a constructor with one input and explicitly copying its properties?
obj.property1 = from.property1;
obj.property2 = from.property2;
etc.
Thanks,
Dani
There is another easy way to create copies of handle objects by using matlab.mixin.Copyable. If you inherit from this class you will get a copy method which will copy all the properties for you.
classdef YourClass < matlab.mixin.Copyable
...
a = YourClass;
b = copy(a); % b is a copy of a
This copy method creates a copy without calling constructors or set functions of properties. So this should be faster. You can also customize the copy behavior by overriding some methods.
If you want a quick-and-dirty solution that assumes all properties can be copied, take a look at the PROPERTIES function. Here's an example of a class that automatically copies all properties:
classdef Foo < handle
properties
a = 1;
end
methods
function F=Foo(rhs)
if nargin==0
% default constructor
F.a = rand(1);
else
% copy constructor
fns = properties(rhs);
for i=1:length(fns)
F.(fns{i}) = rhs.(fns{i});
end
end
end
end
end
and some test code:
f = Foo(); [f.a Foo(f).a] % should print 2 floats with the same value.
You can even use
try
F.(fns{i}) = rhs.(fns{i});
end
which makes the method more useful