How to make calls to static methods independent of packaging structure (name)?

Hello,

I have the following class:

classdef TestStaticMethodPackage

    methods (Static)
        function hello
            fprintf("Hello world\n");
        end

        function write
            TestStaticMethodPackage.hello;
        end
    end

end

I run it:

>> TestStaticMethodPackage.write
Hello world

I am now trying to organize my code into a package:

>> !mkdir +TestPackage
>> !move TestStaticMethodPackage.m +TestPackage\

Trying to run now:

>> TestPackage.TestStaticMethodPackage.write
Unable to resolve the name 'TestStaticMethodPackage.hello'.

Error in TestPackage.TestStaticMethodPackage.write (line 9)
            TestStaticMethodPackage.hello;

This behavior breaks essentially all static methods, and requires the classes to be aware of their external environment. Is there a simple workaround to make it flexible to work in any package structure without having to change all calls where static methods are used?

I was thinking about writing some static method launcher based on dbstack and eval but what's making things worse is that dbstack does not see the package name in front of the class name. Adding the following line before TestStaticMethodPackage.hello; line in class definition:

s = dbstack('-completenames')

results in:

s = 

  struct with fields:

    file: 'C:\...\+TestPackage\TestStaticMethodPackage.m'
    name: 'TestStaticMethodPackage.write'
    line: 9

'name' seems inconsistent, since even within the class itself I need to prepend package name to class name to call a static method.

[Jiri Hajek]

Hi, it seems that you want to run code that is not on the MATLAB path. It is not clear why you should want this, as you can easily "addpath", if its really important for you. You want to build a compiled app and be able to run it anyway or what is the purpose of this?

Also, you are using funny name for your directory (note the "+" sign within the folder name. Matlab is generally sensitive about special characters on the path.

[Robert Borkowski]

Hi Jiri, + is not a "funny name". It is a prefix used to identify a package directory https://www.mathworks.com/help/matlab/matlab_oop/scoping-classes-with-packages.html Packages cannot be added to path using addpath.

Answer 1

[chrisw23]

try to set a session path (addpath) and import the package path (i.e. import MyPackageRoot.TestPackage.*)

[Robert Borkowski]

Hi Chris,

That's not really a solution. In the example above I only have one level of packages: TestPackage, which already is in the working directory.

After running import TestPackage.* I can then of course make calls in the current scope, but it does not solve the fundamental problem of calls to static member method inside of the same classdef, which happen in the scope of another static member method:

>> import TestPackage.*
>> TestStaticMethodPackage.write
9              TestStaticMethodPackage.hello;
Unable to resolve the name 'TestStaticMethodPackage.hello'.

Error in TestPackage.TestStaticMethodPackage.write (line 10)
            TestStaticMethodPackage.hello;
 

The only way I can to solve this problem is to make changes in each and every static method, and do a dynamic import that will include potential hierarchy of pacakges names. It seems to be "broken by design".

[chrisw23]

Path ..MatLabClassExample\+TestPackage\@TestStaticLibrary

TestScript at MatLabClassExample dir

import TestPackage.*
str = "direct static call: " + TestStaticLibrary.hello()

myStaticLib = TestStaticLibrary();
str = "indirect static call: " + myStaticLib.write()

classdef TestStaticLibrary < handle
    events 
        % requires handle super class
    end

    properties (SetAccess = public, GetAccess = public)
        % to be defined
    end

    methods (Access = public)
        function obj = TestStaticLibrary()
            % construcor
        end

        function delete(~)  % ~ replaces unused obj argument here
            % destructor
        end

        %% my public methods
        function str = write(obj) 
            str = obj.hello; 
        end 
    end
    %% private methods
    methods (Access = private)

    end
    %% static methods
    methods (Static)
        function str = hello
            str = "Hello world";
        end
    end
end

Answer 2

[Walter Roberson]

Known work-arounds:

• preprocessing the source code to convert some kind of relative reference to absolute reference before executing
• pass down the package names in calls so that you can dynamically generate the import statements (does not play well with compilation)