Fix CMake variable usage

[wyphan]

CMAKE_MAXIMUM_RANK is now properly defined as a CMake cache variable of type string (even though it functions as an int). Thus, at configure time, it is passed on as cmake -DCMAKE_MAXIMUM_RANK:String=7, for instance.
I only changed the semantics of defining the variable -- use set instead of option -- and updated the README file and CI workflows accordingly.

[awvwgk]

Thanks for sharing. I'm learning something new about CMake every day ;).

I'm intrigued, what is the difference between cached variables and options in CMake? Is there a reason to prefer cached variables over options?

[wyphan]

@awvwgk The online documentation for CMake on option seems to suggest that it is used mainly for boolean ON/OFF values, not for integer data. It has its uses though, as you can see in this StackOverflow page. Don't worry, I'm still learning CMake too!

[wyphan]

Also, the thing that made me recognize the issue in the first place is when I ran cmake-gui. If declared as an option, it shows up a checkmark, instead of a text field where I can input a number.

[jvdp1]

Thank you for this PR. I am learning something too. However, I think that cmake -DCMAKE_MAXIMUM_RANK:String=4 is not really intuitive, and more "complex" than cmake -DCMAKE_MAXIMUM_RANK=4.

Are there any other alternatives?

[wyphan]

The old syntax `-DCMAKE_MAXIMUM_RANK=4` should still work, albeit not "standard-conforming".

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On Sun, Jul 11, 2021, 15:57 Jeremie Vandenplas ***@***.***> wrote: Thank you for this PR. I am learning something too. However, I think that cmake -DCMAKE_MAXIMUM_RANK:String=4 is not really intuitive, and more "complex" than cmake -DCMAKE_MAXIMUM_RANK=4. Are there any other alternatives? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#459 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AMERY5CMW57H6WHD7ZPS25DTXHZTZANCNFSM5AFRYNCQ> .

[jvdp1]

Thank you for your explanations @wyphan . LGTM.

[certik]

Fine with me also.

[jvdp1]

Fine for @certik + 2 approvals, I'll merge.