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

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Ano
Ano 2017-5-23
评论： Rik 2021-8-5
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 .

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采纳的回答

Jan
Jan 2017-5-23
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.
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Steven Lord
Steven Lord 2017-5-23
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;

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更多回答（1 个）

Robert
Robert 2021-2-26
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.
  2 个评论
Florian B
Florian B 2021-8-5
编辑：Florian B 2021-8-5
Would using the reference as
x = Constants.g;
instantiate the object "Constants" though? Or is this a static property?
Rik
Rik 2021-8-5
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.

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