Improve compile time of Flows

[reneSchm]

Changes and Information

A fairly small change to the index_of_type implementation results in a significant reduction in time and memory used during compilation of larger flow models. Tested on the off-repo sde_ui10 that uses ~400 flows, resulting in a speedup of 4 while using 1/5 of the memory. This is a rough measurement using /usr/bin/time on clean compiling the ui10 example, see the attached file for details.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.28%. Comparing base (616cf03) to head (727d82a).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1475      +/-   ##
==========================================
- Coverage   97.31%   97.28%   -0.04%     
==========================================
  Files         187      187              
  Lines       16027    16017      -10     
==========================================
- Hits        15597    15582      -15     
- Misses        430      435       +5     

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[HenrZu]

Thank you for this great addition :) The head-tail iteration is really smart.
I have a few minor comments.

I just checked, and the maximum recursion depth is around 1000 (depending on the compiler). I know that this is a super artificial setup, but maybe its necessary at some point, we should perhaps leave a comment in the file that you can increase it with a flag. What do you think? (Especially considering the ODE model with fully continuous mobility, where we also have the spatial index).

[reneSchm]

I just checked, and the maximum recursion depth is around 1000 (depending on the compiler). I know that this is a super artificial setup, but maybe its necessary at some point, we should perhaps leave a comment in the file that you can increase it with a flag. What do you think?

Maybe it makes sense to mention in the rst documentation that FlowModels with >500 Flows are a questionable idea. But I don't think putting comments on compiler flags deep into the metaprogramming header will be very helpful. But the kind of errors you get when this fails are usually well searchable. Also, you will notice the compile time increase.

I lean towards not writing down anything. Web results are probably easier to find then our text, wherever we put it. Also, the flags vary by compiler (and maybe even version?).