how to make a constant global so all packages files use it?

hello! I would like to define a constant in such a way all my functions in the package folders use it , how can I do it ?? Thank you in advance .

[Stephen23]

The MATLAB documentation clearly states "Best Practice: Passing Arguments", which is also trivially easy:

 k = 1.234;
 myfun(k,...)
 other(k,...)
 morefun(k,...)

The MATLAB documentation also says "Use global variables sparingly, if at all", which is also what many discussions on this forum also advise: https://www.mathworks.com/matlabcentral/answers/319613-how-to-use-global-variable-as-local-variable

http://blogs.mathworks.com/videos/2010/03/08/top-10-matlab-code-practices-that-make-me-cry/

https://www.mathworks.com/matlabcentral/answers/332403-global-variables-in-a-guide-gui

https://www.mathworks.com/matlabcentral/answers/271209-what-is-better-option-than-using-global

etc, etc

Answer 1

[Jan]

As Stephen has explained already, passing variables as arguments is the best practice.

If you have really good reasons to define a constant globally, do not use global, but prefer a dedicated function, which provides the values as struct:

function C = myPackageConstants()
C.g  = 9.81;
C.pi = 3.14159265;
C.VolumeOfHeidelbergBarrel = 221716;  % liter

Then call this from all function as:

C = myPackageConstants;

This is less clear than using arguments. If it is called very often, it might matter that it has a certain runtime overhead. But in opposite to globals, you can be sure that the values are not modified anywhere, such that debugging gets horrible.

[Stephen23]

+1 nice solution

[Steven Lord]

Or if it's a single constant that is broadly usable, like pi, make it a function that returns just that one value. The pi function is built-in, but if it were written as a function file it would be just:

function P = pi
P = 3.14159265358979;

Answer 2

[Robert]

You could also define a class with only constant properties. Contrary to Jan's solution, you can access the constants directly, without having to assign all of them to a variable first.

Calling it many times does not result in runtime overhead, like Jan said might be the case for his solution.

classdef Constants
    properties (Constant)
        g = 9.81
        k = 1.234
    end
end

Reference the constants using:

Constants.g

Of course, if the Constants class is in one of your packages, you have to include its namespace in the call.

[Florian B]

Would using the reference as

x = Constants.g;

instantiate the object "Constants" though? Or is this a static property?

[Rik]

It is a static property for most intents and purposes.

You could easily see if multiple calls of this type will call the constructor multiple times by putting a disp in the constructor.