[common] C++20 Concepts for ponca

[BDoignies]

Hi,

This PR serves as a base for introducing concepts in the library. Note that it depends on #219 but some commits will drop once rebase.

This first commit introduces:

• A format for requires clause
• An example concept for points. Note that due to PointBinding type, we can not check for return type, for write access or for a non const version.

I suggest to start concept by the prefix "Is" or "Provides" because of current Ponca terminology.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.20%. Comparing base (cfb0fcc) to head (6acec21).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #293      +/-   ##
==========================================
+ Coverage   94.10%   94.20%   +0.10%     
==========================================
  Files          86       84       -2     
  Lines        3340     3315      -25     
  Branches      264      263       -1     
==========================================
- Hits         3143     3123      -20     
+ Misses        196      191       -5     
  Partials        1        1              

Files with missing lines	Coverage Δ
Ponca/src/Fitting/algebraicSphere.h	96.61% <ø> (ø)
Ponca/src/Fitting/algebraicSphere.hpp	100.00% <ø> (ø)
Ponca/src/Fitting/basket.h	100.00% <ø> (ø)
Ponca/src/Fitting/basketUnit.h	96.96% <ø> (ø)
Ponca/src/Fitting/cnc.h	100.00% <ø> (ø)
Ponca/src/Fitting/covarianceFit.h	100.00% <ø> (ø)
Ponca/src/Fitting/covarianceFit.hpp	94.11% <ø> (ø)
Ponca/src/Fitting/covarianceLineFit.h	85.71% <ø> (ø)
Ponca/src/Fitting/covariancePlaneFit.h	100.00% <ø> (ø)
Ponca/src/Fitting/covariancePlaneFit.hpp	94.73% <ø> (ø)
... and 27 more

... and 1 file with indirect coverage changes

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[BDoignies]

Hi,

I added a few more concepts. There are things that we can not check with concept unfortunately.

For example, ProvidesMeanPosition should require barycenterLocal to be defined. However, this is intentionally protected so concept can not check this as this is not accessible.

We can try a work around using a subclass but I am not sure this is worth doing.

[BDoignies]

Another conflict:

-> Ponca::Plane has an isApprox function inherited through 'Eigen::Hyperplane'
-> AlgebraicSphere requires an isApprox function from an AlgebraicSphere

Therefore, when a fitting is instantiated with both, one isApprox hides the other. In the case I found this, Planes::isApprox hides AlgebraicSphere::isApprox and fails the ProvidesAlgebraicSphere concept.

We can not trick the compiler beacause AlgebraicSphere::isApprox is templated on 'any' type, hence we can not use an empty initializer... Because there are overload (although hidden), we can not check for '&T::isApprox' pattern...

[BDoignies]

Hi,

Here are a few more concepts.

What's left:

• Monge Patch: Not clear what its definition would be
• HeightField: I do not have access to it's base. I can not write a concept that requires a derivation from it...
• Test to verify all concepts were properly instantiated and that they fail when required
• Add a macro to simplify requirements
• static_assert in requirements clause wherever possible
• Remove curvature.h. This should be in another PR though

Questions:

• For Weingarten map what would be the proper cast name ? wiengartenMap is already taken by the function
• covarianceFit base offers a lot more than its current definition. Should we add the function in the requirements ?

[nmellado]

I gave it a go and modified the current proposition. I also modified the curvature estimator, as I believe it is an important feature.
I did not tried to solve the issues you mentioned in the comments for the missing concepts, will work on it later.
We also need to work on the documentation, I put some comments here and there, but it can definitely be improved.