Hashable Configurations

[danjujan]

Our configurations are currently not hashable because they contain mutable objects, e.g dict or list. Therefore, they cannot be used as a key in a dict or as element in a set which limits their usability.
For example, in my other PR #718 I need a mapping from Configuration -> Reports. Currently my workaround was to rewrite my own immutable configuration class to make that work: https://github.com/se-sic/VaRA-Tool-Suite/pull/718/files#diff-46ee8773a540aedfd0d1cfbb2d2721a6191d64d3868c538d282c34f85a048492R50. But that basically duplicates functionality and it would be nice to reuse our existing configuration classes for that.
However, a lot of our code relies on the mutability of configurations. Therefore, my proposal is to keep configurations mutable by default but make them immutable (freeze them) on demand. The immutables.map datatype provides these properties.

The committed code is a rough and far from perfect sketch how such a solution could look like. Apart from loosing the insertion order of configuration options it passes all tests. But I would like to collect some opinions first before pursuing this.

[boehmseb]

If hashing is the only issue, it should be easier to simply add a custom __hash__() function to the ConfigurationImpl class.
Depending on our requirements, hash(frozenset(__config_values.items())) should suffice as a hashing function.
This should be stable as long as you stay in the same python process. Also see this SO for more discussion regarding this topic: https://stackoverflow.com/questions/5884066/hashing-a-dictionary

[codecov]

Codecov Report

Patch coverage: 91.08% and project coverage change: +0.11 🎉

Comparison is base (93e3f71) 67.43% compared to head (ae07531) 67.54%.

Additional details and impacted files

@@             Coverage Diff              @@
##           vara-dev     #789      +/-   ##
============================================
+ Coverage     67.43%   67.54%   +0.11%     
============================================
  Files           322      322              
  Lines         24459    24590     +131     
============================================
+ Hits          16493    16610     +117     
- Misses         7966     7980      +14     

Impacted Files	Coverage Δ
varats-core/varats/base/configuration.py	89.59% <82.92%> (-6.87%)	⬇️
tests/base/test_configuration.py	100.00% <100.00%> (ø)
tests/mapping/test_configuration_map.py	100.00% <100.00%> (ø)

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[danjujan]

After discussing with @vulder I added a freeze and unfreeze function and deepcopy between them to guarantee immutability.
The other changes are usability improvements.

[vulder]

freezing impl looks fine to me, just suggested a bit of clean up

However, should we maybe add tests for the new FrozenConfiguration?

[vulder]

freezing impl looks fine to me, just suggested a bit of clean up

However, should we maybe add tests for the new FrozenConfiguration?

[vulder]

freezing impl looks fine to me, just suggested a bit of clean up

However, should we maybe add tests for the new FrozenConfiguration?

[vulder]

Looks like github has some issues currently... Somehow it registered by review twice