Inheritance of classes inside a package

Hi,

I have run into problems when using class inheritance in combination with packages. I think it is the same issue as already asked in MATLAB newsgroup a few years ago.

First, suppose I have a bunch of files with the following structure:

./InnerClass.m
./OuterClass.m

and the following conents:

-- InnerClass.m :
classdef InnerClass
end

-- OuterClass.m :
classdef OuterClass < InnerClass
end

Now, being in the . directory, when I issue the command:

>> obj = OuterClass

I get the following answer:

obj = 
  OuterClass with no properties.
  Methods, Superclasses

So far, so good, it works as expected.

Let's move the classes into a package, so that we would have the following structure:

./+package/InnerClass.m
./+package/OuterClass.m

Now, being in the . directory, the command

>> obj = OuterClass

ends up with an error. Of course, now the classes are part of package, we have to call it this way:

>> obj = package.OuterClass

But, GEEEEZ, I got another error message!!!

??? Error using ==> package.OuterClass
The specified super-class 'InnerClass' contains a parse error or cannot be found on MATLAB's search path, possibly shadowed by
another file with the same name.

QUESTION 1: Is this the expected behavior? If yes, what am I doing wrong???

Ok, so it seems that the OuterClass inside package somehow cannot see the definition of the InnerClass. Well, OK, so when I change the current working directory to be the +package directory and try to create the object from there, everything should work as in the beginning, right?

>> cd +package
>> obj = OuterClass
??? Undefined function or variable 'OuterClass'.

WHAT!?!?!

Question 2: Is this the expected behavior? Does the situation of the package directory being the working directory somehow change the way the source files are processed?

Question 3: I work in R2009a, is it the same in the newer versions?

I feel completely puzzled! These are really basic things and I do not understand them. Can somebody help me???

Thanks a lot,

Petr

Answer 1

[Titus Edelhofer]

Hi Petr,

interesting, I haven't tried this. What works is to treat InnerClass as part of the package, i.e.

classdef OuterClass < package.InnerClass

Then it should work. Whether functions/classes inside the package should be "freed" from the necessity to do so, I don't know ... By the way: package directory should not be the working directory, that makes things more complicated then necessary.

Titus

[Petr Posik]

Hi Titus.

Thanks for the answer, that works. But it also means that the OuterClass must know that it is placed in the |package|. Well, this is not unusual, in Java you have to specify the package of the current file using

package packagename;

But it still seems to me a bit strange that a file must know in what package(s) it is placed... :-(

Answer 2

[Daniel Shub]

This seems to me to the documented (although maybe not expected) behavior.

Quesiton 1: The documentation of calling a package method within the package:

http://www.mathworks.com/help/techdoc/matlab_oop/brfynt_-1.html#br_lltt

says that you must use the "package." notation.

Question 2: The documentation on "Packages and the MATLAB Path" is pretty clear:

http://www.mathworks.com/help/techdoc/matlab_oop/brfynt_-1.html#brfynt_-3

that being in the package directory doesn't do much.

Question 3: The documentation is from r2011a, so yes, it is the same in the newer version.

[Petr Posik]

Huh, Daniel, and I thought I have read the docs quite thoroughly! Thanks for the pointers!

[Ron Lu]

That is lame. If I write my classes first, then separate them into different packages, I have to go back to add package name dot (or import *) anywhere the class is referred.

[Daniel Shub]

@Ron, I would suggest you file an enhancement request if you would like to see a change.