💥Require unit enum types to also be struct

[angularsen]

Change all where TUnitType : Enum generic type constraints to include struct constraint, to avoid usages like this.

UnitsNetSetup.Default.UnitParser.Parse<LengthUnit>("abc"); // Ok
UnitsNetSetup.Default.UnitParser.Parse<Enum>("abc"); // Compiles, but throws exception

This also fixes inconsistency, between UnitAbbreviationsCache.GetUnitAbbreviations<TUnitType> and UnitAbbreviationsCache.GetDefaultAbbreviation<TUnitType>.

Changes

• Add struct constraint to all Enum constraints
• Remove two test cases MapAndLookup_MapWithSpecificEnumType_LookupWithEnumType, MapAndLookup_WithEnumType

Noteworthy

There are some minor use cases for passing non-generic Enum value, like getting unit abbreviations for an IQuantity such as UnitAbbreviations.GetDefaultAbbreviation(quantity.Unit).
After this PR, you now have to do GetDefaultAbbreviation(quantity.Unit.GetType(), Convert.ToInt32(quantity.Unit)) instead.
GetAbbreviations() already had this requirement, so now it's more consistent at least.

Sources

https://stackoverflow.com/a/74773273
https://devblogs.microsoft.com/premier-developer/dissecting-new-generics-constraints-in-c-7-3/

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 86%. Comparing base (8b3696b) to head (28a2613).
Report is 1 commits behind head on release/v6.

Files with missing lines	Patch %	Lines
UnitsNet/QuantityDisplay.cs	0%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           release/v6   #1472   +/-   ##
==========================================
  Coverage          86%     86%           
==========================================
  Files             298     298           
  Lines           30515   30515           
==========================================
  Hits            26405   26405           
  Misses           4110    4110           

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[lipchev]

This is great, introducing the struct constraint here opens up the possibility for using
Unsafe.As<TUnit, int>(ref unit)
instead of
Convert.ToInt32(unit)
which is ~34x faster on net8.0 and ~92x faster on net48 🚀

[angularsen]

Sounds good!

[lipchev]

This one is really bugging me with it's 0% coverage - I'm definitely going to do something about it soon..

[lipchev]

If we want to be really strict about it, we should consider making the QuantityInfo class abstract- this way we know that the user won't be able to implement IQuantity without having actually implemented IQuantity<TUnit>.

[lipchev]

This all looks great. Just one question - do you have a preference with the way that the generic constraints are positioned (same line or new line)?

[angularsen]

This all looks great. Just one question - do you have a preference with the way that the generic constraints are positioned (same line or new line)?

Great! No, I'm too old to care about these things anymore 😅 Yolo!
As long as it's follows most typical c# norms, I'm happy.