Is there exist() functionality for packages/namespaces?

Question

Chris 2023-1-6

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https://ww2.mathworks.cn/matlabcentral/answers/1889757-is-there-exist-functionality-for-packages-namespaces

回答： Ashley Trowell 2023-10-26

https://www.mathworks.com/help/matlab/matlab_oop/scoping-classes-with-packages.html

Create a package and put it somewhere in Matlab's path. If you know the parent directory, you could use exist('/path/+package'), but you don't need to know the path to use the package, so that's silly.

The current best solution I have is to try/catch calling a function in the package.

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Answer 1

Ashley Trowell 2023-10-26

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https://ww2.mathworks.cn/matlabcentral/answers/1889757-is-there-exist-functionality-for-packages-namespaces#answer_1341391

There is, but it is hidden. Mathworks doesn't encourage packages and namespaces.

Reference: meta.package.fromname

Create this lambda function:

packageExists = @(pkgName) ~isempty(meta.package.fromName(pkgName));

Then run

pkgExist = packageExists('myPkg');

A nice utility is here that just adds the functionality the the exist function, which is what Mathworks should do.

https://www.mathworks.com/matlabcentral/fileexchange/51573-existp-str-typestr

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Answer 2

Walter Roberson 2023-1-6

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在 MATLAB Online 中打开

You can exist() a function inside the package

exist('matlab.internal.lang.capability.Capability')
ans = 8
which matlab.internal.lang.capability.Capability
/MATLAB/toolbox/matlab/capabilities/+matlab/+internal/+lang/+capability/Capability.m  % matlab.internal.lang.capability.Capability constructor

You can also which the + form of a function (but not the package itself)

which +matlab/+internal/+lang/+capability/Capability
/MATLAB/toolbox/matlab/capabilities/+matlab/+internal/+lang/+capability/Capability.m  % matlab.internal.lang.capability.Capability constructor
which +matlab/+internal/+lang/+capability
'+matlab/+internal/+lang/+capability' not found.

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Chris 2023-1-7

编辑：Chris 2023-1-7

在 MATLAB Online 中打开

The difference compared to my package would be that the classdef file is not in an @ folder, but in the package root. So it's another example of

exist package.Class

that works.

I wouldn't expect a class method to be available to exist or which (though it turns out they can be found if treated as files), so that just leaves the package itself (I can live without that, I guess), and functions in the +folder--which are the one thing treated differently between which and exist.

Walter Roberson 2023-1-7

Class methods can be found using which, but sometimes they will not be located unless the class has been loaded at least once in this session (since the last clear classes)

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