In this article (https://blogs.mathworks.com/loren/2012/07/16/who-what-why-but-not-this/) near the bottom Loren says that class properties can be the same as keywords. However, how is this possible? If you write a classdef script any attempt to use a keyword (including class keywords like "events") in the properties block gets a red syntax error. Was she mistaken? I'm asking because I really want a property name to be a keyword for a particular application.
Its possible by the use of dynamic properties, for example:
classdef test < dynamicprops
methods
function obj = test()
end
end
end
var = test();
var.addprop ( 'events' );
var.events = 123;
It can make code harder to maintain and its a bit overkill if you only want to name a single property the same as a keyword, in that instance why dont you do something like capitilizing the var name, or prepending it with something - so it still reads like what you want but it doesn't cause the name clash:
classdef test
properties
Events
myIf
% etc...
end
methods
function obj = test()
end
end
end
Related
I would like to access the class name of the concrete class that's invoking a static method implemented in an abstract superclass.
This is the code (part of) of the abstract superclasss:
classdef (Abstract) AbstractJobProcessor < handle
properties (Abstract, Constant)
VERSION_MAJOR;
VERSION_MINOR;
LAST_MODIFIED;
end
...
methods (Static)
function res = getVersionMajor;
res = AbstractJobProcessor.VERSION_MAJOR;
end
function res = getVersionMinor
res = AbstractJobProcessor.VERSION_MINOR;
end
function res = getVersionInfo
res = sprintf('**CLASSNAME**: v%d.%02d (last modified: %s)',...
AbstractJobProcessor.VERSION_MAJOR,...
AbstractJobProcessor.VERSION_MINOR,...
AbstractJobProcessor.LAST_MODIFIED);
end
end
...
Basically, I would like to access the classname of the concrete subclass and use it in the method getVersionInfo in place of the string **CLASSNAME**.
All the methods returning meta information about a class (that I have found in the documentation) require a reference to an instance of the class (like, for example, mc = metaclass(object)).
The below function will give you what you want - subclass name, that was used when invoking an (inherited) static superclass method. Just call it inside your superclass method like you would any normal function:
className = getStaticCallingClassName();
What it does handle:
Both the case when method was invoked programmatically (i.e. by a running script / function), as well as when it was invoked from the command window.
Arbitrarily nested package names (i.e. classes located inside directories prefixed with +).
What it does not handle:
Does not work if the static method is called in a non-static context, i.e. on an object instance. But you should not be using such syntax anyway. This would've been possible if we were able to use evalin with 'caller' workspace recursively, but it does not work this way.
A brief explanation behind the idea: second entry in the stack trace, produced by dbstack, would correspond to the superclass, which we can use to extract the static method name. The next steps depend on:
If the method is invoked programmatically, third stack entry would point us to a line in the the parent script/function which we need to read, e.g. using dbtype. All that's left to do is extract the subclass name using regexp based on the method name.
If the method is invoked from command window, we query the last command and use that as the input for our regular expression.
Note that even if stack has 3 entries or more, it doesn't mean that the method was invoked programmatically. For example, if we've stopped on a breakpoint somewhere and invoke the method from command window, stack trace would be long, but regexp based on the line from the third stack trace entry will not give us the answer. In this case we fall back to the command window approach.
Warning: it heavily relies on undocumented features and may break in any feature release. Tested on Matlab 2015b, but should work on most previous releases as well. Some may say it is quite dirty, but it works very well, and it's the only method that I'm aware of to achieve such a behavior.
function [className, fullPath] = getStaticCallingClassName()
ST = dbstack('-completenames');
% First one is getStaticCallingClassName, second one is the superclass
methodName = char(regexp(ST(2).name, '[^\.]([^.]*)$', 'match'));
% matches string (combination of alphanumeric/underscore/dot characters) preceeding the given method call.
pattern = sprintf('[\\w.-]*(?=.%s)', methodName);
% If the parent called static method programmatically, we should be able to find it via the next (third) stack trace
if length(ST) > 2
command = evalc('dbtype(ST(3).file, num2str(ST(3).line))');
className = char(regexp(command, pattern, 'match'));
else % was likely called from command window. Long stack trace means that we're simply waiting in a breakpoint somewhere
className = []; % go straight to command window approach
end
if isempty(className) % means that static method was called directly from command window
javaHistory = com.mathworks.mlservices.MLCommandHistoryServices.getSessionHistory();
command = char(javaHistory(end));
className = char(regexp(command, pattern, 'match'));
end
fullPath = which(className);
end
Here's a workaround. According to the MATLAB documentation:
'Ordinary methods define functions that operate on objects of the class',
'Static methods are (1) associated with a class, but (2) not with specific instances of that class'.
You can have both aspects of static methods if you call an ordinary method with an empty object array.
For example, suppose we have a base class:
classdef base
methods
function obj = base()
disp('constructor called')
end
function dispClassName(obj)
disp(['class name = ', class(obj)]);
end
end
end
and a subclass
classdef sub < base
end
Now call the methods as follows (this will not invoke any constructor):
>> base.empty.dispClassName
class name = base
>> sub.empty.dispClassName
class name = sub
A real solution (for which I did an enhancement request 03315500 to MathWorks) would be to extend the MATLAB language with a method attribute 'Class' to define methods that are associated with the invoking class (similar to the Python #classmethod decorator). Methods of this class would automatically receive the metaclass of the invoking function as a first argument. With such an extension we could define a base class:
% Future MATLAB syntax extension
classdef base
methods(Class) % New method attribute ‘Class’
function dispClassName(cls) % implicit argument (meta.class)
disp(['class name = ' cls.Name ]);
end
end
end
and a subclass
classdef sub < base
end
and call
>> base.dispClassName
class name = base
>> sub.dispClassName
class name = sub
I'm trying to grab a method handle from within an object in MATLAB, yet something in the sort of str2func('obj.MethodName') is not working
The answer is to get a function handle as #Pablo has shown.
Note that your class should be derived from the handle class for this to work correctly (so that the object is passed by reference).
Consider the following example:
Hello.m
classdef hello < handle
properties
name = '';
end
methods
function this = hello()
this.name = 'world';
end
function say(this)
fprintf('Hello %s!\n', this.name);
end
end
end
Now we get a handle to the member function, and use it:
obj = hello(); %# create object
f = #obj.say; %# get handle to function
obj.name = 'there'; %# change object state
obj.say()
f()
The output:
Hello there!
Hello there!
However if we define it as a Value Class instead (change first line to classdef hello), the output would be different:
Hello there!
Hello world!
One could also write
fstr = 'say';
obj.(fstr)();
This has the advantage that it does not require a handle class to work if the object (obj) is modified.
Use #. The following code works for me:
f = #obj.MethodName
No other answer mimics str2func('obj.MethodName'). Actually, this one doesn't either, not exactly. But you can define an auxillary function like so:
function handle = method_handle(obj, mstr)
handle = #(varargin) obj.(mstr)(varargin{:});
end
Then method_handle(obj, 'MethodName') returns a handle to obj.MethodName. Unfortunately, you cannot pass the variable name of obj as a string - eval("obj") will be undefined in the function's scope.
I'm trying to change a property in a class called houses via a utility method which is Static. I'm getting terribly confused with the reference obj as I don't know when and where it should be used. I am trying to bypass the constructor method so I can access the setProperty method, but I am getting errors such as too many output arguments. I've tried passing in obj as well as x, but I get similar errors. However, I can change the property a if I pass in a value to the constructor method.
classdef houses
properties
a;
end
methods
% constructor method
function obj = houses()
end
end
methods (Static)
function setProperty(x)
obj.a = x;
end
end
end
In general, you should not use static methods to set properties of a class. If your property is public, then you can use a static method but it is highly recommended that you do not. If your property is private/protected, then you definitely cannot use a static method to modify it.
Your class should look like this then (I took the liberty of stating explicitly the access properties of each block):
classdef houses
properties (Access = private)
a;
end
methods (Access = public)
% constructor method
function obj = houses()
end
function SetA(obj, a)
obj.a = a;
end
function DoSomething(obj, more_parameters)
% Lengthy stuff here
end
end
end
Now, regarding your question about obj: the answer is you must pass obj as the first argument of every instance method. The variable obj refers to the current instance of the class in a generic way. See for example the method DoSomething.
Static methods do not have access to any of the properties of the class, unless public. As such, when declaring a static method, you should not pass the obj variable.
Last thing: always use explicit access modifiers for your properties and methods. It will save you some headaches.
A static method is not typically supposed to access an object (hence it does not have access to obj).
If you want to modify a static propperty (shared by all objects, and the class itself), you can use something like:
classdef houses
properties (Static)
a;
end
methods
% constructor method
function obj = houses()
end
end
methods (Static)
function setProperty(x)
houses.a = x;
end
end
end
Regarding obj, it is the 1st argument of every methods (non static). So when you do:
o = myClass();
o.myMethod(args);
Matlab will see this as:
myMethod(o, args);
So when you define the method, you have to put obj as the 1st argument (in fact you can choose any name, it does not have to be obj).
I implemented a class in Matlab which derives from matlab.mixin.Copyable. I want to suppress the output of the command window so that the user does not has information about the class. I want to do this for security reasons. For example:
a = myStack;
a
ans=
myStack with no properties.
But the user can click myStack and it gives information about the class. I know that I can overload display for this, but the behavior that I want is like follows:
b = handle(1);
b
ans=
handle
How I can do this?
Thanks.
You have to derive from matlab.mixin.CustomDisplay interface and override the getPropertyGroups method.
For the specific purpose of removing the link to help in the header, also override getHeader method.
NB: I don't see how you can truly handle security in this way. Users will still have other means to get details about your class. For instance meta = ?MyClass, or just edit MyClass if not encrypted with pcode, or simply in the editor just typing myInstance. and let intellisense list all non hidden/private methods and properties.
Example for the display you want to have:
classdef foo < matlab.mixin.CustomDisplay
properties
Login = 'root';
Password = '1234'
end
methods (Access = protected)
function [str] = getHeader(obj)
str = mfilename;
end
function [pg] = getPropertyGroups(obj)
pg = [];
end
function [str] = getFooter(obj)
str = sprintf('\n');
end
end
end
May be better solution to avoid displaying some properties (including from help-link):
classdef foo < matlab.mixin.CustomDisplay
properties (SetAccess = private, GetAccess = private) % here remove any public access, use '(Hidden)' if only want to remove from display and help
Login = 'root';
Password = '1234'
end
end
NB: Careful, as #Daniel wrote, whatever you will do, struct(a) reveals all property names and values.
As well as the method from #CitizenInsane, you may get what you want by simply adding the Hidden = true attribute to some or all of your properties.
Reiterating what others have said, though, if you're doing this in order to seriously prevent people from understanding the internals of your class, struct(a) will always show them the properties. You can overload your class with a struct method that errors out, but then builtin('struct', a) would still do the original thing. Also ?Classname will provide meta-information about the class that includes its properties.
In the following piece of code, the destructor of class TdcTestResult is called at the end of function add, and so method variable mTdcTestResults will become empty again.
How can I make the instance of TdcTestResult inside mTdcTestResults persistent?
classdef Tdc
properties % (Access = private)
mTestRun = TdcTestRun;
mTestResults = [];
end
methods(Access = public)
function add(obj, componentSerialNumber, testName, testVersion, paramName, unitOfMeasureCode, paramScale, paramLimitTypeCode, paramLowerLimit, paramUpperLimit, responseValue, folderPath, isFailed, isOverridden, overriddenReason)
if(nargin > 0)
obj.mTestResults = [obj.mTestResults TdcTestResult];
obj.mTestResults(end).set(componentSerialNumber, testName, testVersion, paramName, unitOfMeasureCode, paramScale, paramLimitTypeCode, paramLowerLimit, paramUpperLimit, responseValue, folderPath, isFailed, isOverridden, overriddenReason);
obj.mTestRun.addTestResult(obj.mTestResults(end));
end
end
end
end
I think the actual issue is that you're effectively not changing obj.
If you would, the reference to the new TdcTestResult inside mTestResults should prevent the destructor from being called.
This is connected to Danial R's answer:
If you don't implement Tdc as a handle subclass, your add method has to return the modified obj.
Otherwise the changed you make inside add are lost.
So you'll either have to return obj and modify your calling syntax to
tdcObject = tdcObject.add(...);
or inherit from handle - which is probably the better alternative.
TdcTestResult needs handle to be a superclass, otherwise your code can not work. More details in the documentation
If this does not help, please include an executable example of code.