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Redesign UnitSystem to support non-SI systems and configurable default units #709

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@lipchev lipchev commented Sep 28, 2019

(WIP) for #651

  • 1. Redesign/Remove BaseUnits type and remove related from JSON and UnitSystem (breaking change)

  • 2. UnitSystem: Add mapping of default unit, such as QuantityType.Length => LengthUnit.Centimeter

  • 3. UnitSystem: Add mapping of default abbreviation per unit enum value, such as LengthUnit.Feet => "ft" (optional- also a breaking change if UnitAbbreviationCache is to become part of the UnitSystem)

  • 4. Length.ctor(double, UnitSystem) constructs with unit system's default unit for Length

  • 5. double val = myLength.As(UnitSystem) converts to unit system's default unit for Length

  • 6. UnitSystem should remain immutable, so to change its configuration at runtime you create a new instance either manually or by cloning an existing system with extension methods for adding/modifying mappings like in use case 5. Then you inject this instance into your view or whatever.

  • 7. Add UnitSystem.SI and UnitSystem.EnglishEngineering with mappings

  • 8. Add tests for the the new public methods in UnitSystem (got one in LenghtTests- but none that test for the "exceptional" cases)

…stem

- UnitSystem holds the list of default units for each (compatible?) quantity type and a method (GetDefaultUnitInfo) that provides the corresponding UnitInfo given a QuantityType
- All methods in Quantity that use a UnitSystem now use the new GetDefaultUnitInfo
- Added a method (in UnitSystem) for creating derived unit systems(WithDefaultUnit), providing a new QuantityType->UnitInfo association and optionally a new BaseUnits definition (as currently used by Equals and visible in public ctor- otherwise obsolete?)
@lipchev lipchev changed the title Create QuantityType -> UnitInfo associations (DefaultUnits) in UnitSy… Create QuantityType -> UnitInfo associations in UnitSystem Sep 28, 2019
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codecov-io commented Sep 28, 2019

Codecov Report

Merging #709 (e45efe8) into master (0f39bec) will increase coverage by 84%.
The diff coverage is 83%.

❗ Current head e45efe8 differs from pull request most recent head dfe0bd2. Consider uploading reports for the commit dfe0bd2 to get more accurate results

@@            Coverage Diff            @@
##           master    #709      +/-   ##
=========================================
+ Coverage        0     84%     +84%     
=========================================
  Files           0     308     +308     
  Lines           0   43886   +43886     
=========================================
+ Hits            0   36938   +36938     
- Misses          0    6948    +6948     
Impacted Files Coverage Δ
...tsNet/GeneratedCode/Quantities/AmplitudeRatio.g.cs 79% <80%> (ø)
UnitsNet/GeneratedCode/Quantities/Angle.g.cs 83% <80%> (ø)
...tsNet/GeneratedCode/Quantities/ApparentEnergy.g.cs 79% <80%> (ø)
...itsNet/GeneratedCode/Quantities/ApparentPower.g.cs 79% <80%> (ø)
UnitsNet/GeneratedCode/Quantities/AreaDensity.g.cs 76% <80%> (ø)
.../GeneratedCode/Quantities/AreaMomentOfInertia.g.cs 80% <80%> (ø)
UnitsNet/GeneratedCode/Quantities/BitRate.g.cs 86% <80%> (ø)
...dCode/Quantities/BrakeSpecificFuelConsumption.g.cs 79% <80%> (ø)
UnitsNet/GeneratedCode/Quantities/Capacitance.g.cs 81% <80%> (ø)
...Code/Quantities/CoefficientOfThermalExpansion.g.cs 79% <80%> (ø)
... and 354 more

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lipchev commented Sep 28, 2019

Initially I went with a dictionary (as proposed in #651) but being stunned by the lack of improvement in performance compared with the test in #708 I dropped it in favor of an array (of QuantityInfo), indexed by the (int)QuantityType - 1, which gave me some improvement- but not nearly as much as I expected initially..

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lipchev commented Sep 28, 2019

Method Mean Error StdDev Median Gen 0 Gen 1 Gen 2 Allocated
Constructor 10.261 ns 0.2568 ns 0.3683 ns 10.102 ns - - - -
Constructor_SI 341.489 ns 20.1771 ns 57.5664 ns 300.000 ns - - - -
FromMethod 23.169 ns 0.1087 ns 0.0907 ns 23.156 ns - - - -
ToProperty 7.105 ns 0.0894 ns 0.0836 ns 7.111 ns - - - -
As 7.171 ns 0.1547 ns 0.1447 ns 7.095 ns - - - -
As_SI 336.364 ns 19.1489 ns 56.1604 ns 300.000 ns - - - -
ToUnit 16.206 ns 0.1705 ns 0.1424 ns 16.205 ns - - - -
ToUnit_SI 456.667 ns 23.4713 ns 65.4286 ns 400.000 ns - - - -
ToStringTest 2,022.562 ns 14.2156 ns 13.2973 ns 2,020.125 ns 0.1945 - - 832 B
Parse 51,561.651 ns 990.9471 ns 1,179.6520 ns 51,123.584 ns 10.1929 - - 43000 B
TryParseValid 49,676.343 ns 808.6956 ns 756.4544 ns 49,425.769 ns 10.1929 - - 42976 B
TryParseInvalid 52,532.164 ns 612.5532 ns 543.0125 ns 52,483.185 ns 10.1318 - - 42576 B
QuantityFrom 68.093 ns 1.4228 ns 1.5814 ns 67.222 ns 0.0132 - - 56 B
IQuantity_As 15.401 ns 0.2076 ns 0.1942 ns 15.320 ns 0.0057 - - 24 B
IQuantity_As_SI 380.723 ns 14.8686 ns 39.6873 ns 400.000 ns - - - -
IQuantity_ToUnit 23.538 ns 0.2679 ns 0.2506 ns 23.453 ns 0.0133 - - 56 B
IQuantity_ToStringTest 2,037.505 ns 39.4539 ns 61.4250 ns 2,013.519 ns 0.1945 - - 832 B

Note that the performance of my machine is slightly lower today (I think it's either the room temperature or some process eating up my resources).

- updated the comments and invalid arguments checks
- added a few tests for those cases

a few question marks remain (marked with TODOs)
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lipchev commented Sep 29, 2019

Still some things I'm not sure about:

  • what would be the expected equality comparison for two UnitSystems (currently depends on the BaseType)
  • previous tests state that for example "AmplitudeRatio is unitless. Can't have any matches" (when constructing AmplituedRatio using SI)- yet it seems there are 4 "dimensionless units" to chose from when selecting a default unit
  • I struggled to validate within WithDefaultUnit(QuantityType, UnitInfo) that UnitInfo corresponds to the provided QuantityType (any ideas? lookup the list of Info's again? change the signiture?)
  • I struggled to create the generic overload corresponding to WithDefaultUnit(QuantityType, UnitInfo):
    WithDefaultUnit<TUnit>(UnitInfo<TUnit>) // how do I get the QuantityType value from this

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We can't merge this into master branch until all breaking changes are ready, so I just created release/v5 branch. Please point this PR to that branch instead, or create a new PR if it can't be changed.

Other breaking changes: #666

@angularsen angularsen added this to the 5.0 milestone Sep 29, 2019
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which gave me some improvement- but not nearly as much as I expected initially..

I think this basically comes down to the fact that we have ~100 quantities today, and enumerating 100 items with a simple condition check is really really fast to begin with. At any rate, a lookup of sorts seems reasonable anyway.

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angularsen commented Sep 29, 2019

Still some things I'm not sure about:

  • what would be the expected equality comparison for two UnitSystems (currently depends on the BaseType)

I propose using the default implementation that class brings, which checks if they are the exact same object reference. We could compare all the mappings and any values, but I really question the value of this.

  • previous tests state that for example "AmplitudeRatio is unitless. Can't have any matches" (when constructing AmplituedRatio using SI)- yet it seems there are 4 "dimensionless units" to chose from when selecting a default unit

I believe you are referencing this test:
https://github.com/angularsen/UnitsNet/blob/master/UnitsNet.Tests/CustomCode/LengthTests.cs#L189-L194

First, I don't understand why we are testing AmplitudeRatio in LengthTests.
Second, it's likely a limitation of the old unit system design where it's not possible to uniquely map from SI base units to dimensionless units. I don't see why we shouldn't preserve this behavior in the new design, so this test can be removed I think.

  • I struggled to validate within WithDefaultUnit(QuantityType, UnitInfo) that UnitInfo corresponds to the provided QuantityType (any ideas? lookup the list of Info's again? change the signiture?)

I'll have to look closer on this one.

  • I struggled to create the generic overload corresponding to WithDefaultUnit(QuantityType, UnitInfo):
    WithDefaultUnit<TUnit>(UnitInfo<TUnit>) // how do I get the QuantityType value from this

I'll have to look closer on this one.

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I know this is work in progress, but here are some early comments after reading through the first time.

{
// TODO do we expect to preserve this behavior?
// AmplitudeRatio might be unitless- but there are (more than one) ways to express ratios.
Assert.Null(UnitSystem.SI.GetDefaultUnitInfo(AmplitudeRatio.QuantityType));
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  1. Preserve returning null if no mapping is defined.
  2. AmplitudeRatio should have a mapping defined in SI, I think.

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Right- so, in theory, the only way to get a null here would be if one creates a custom unit system, explicitly setting the association to null (as presumable the original unit system would have all of its associations defined).

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Sounds about right. We should also create some unit tests that breaks as soon as a new quantity is added and if one forgets to add a mapping of default unit for included unit systems such as SI and EnglishEngineering. I don't think we need to add a mapping for default abbreviation, since I think it's natural to default to the first abbreviation defined in JSON as we already do.

UnitsNet.Tests/CustomCode/LengthTests.cs Show resolved Hide resolved
UnitsNet.Tests/UnitSystemTests.cs Outdated Show resolved Hide resolved
UnitsNet.Tests/UnitSystemTests.cs Outdated Show resolved Hide resolved
[InlineData(LengthUnit.Meter, MassUnit.Kilogram, DurationUnit.Second, ElectricCurrentUnit.Ampere, TemperatureUnit.Undefined, AmountOfSubstanceUnit.Mole, LuminousIntensityUnit.Candela)]
[InlineData(LengthUnit.Meter, MassUnit.Kilogram, DurationUnit.Second, ElectricCurrentUnit.Ampere, TemperatureUnit.Kelvin, AmountOfSubstanceUnit.Undefined, LuminousIntensityUnit.Candela)]
[InlineData(LengthUnit.Meter, MassUnit.Kilogram, DurationUnit.Second, ElectricCurrentUnit.Ampere, TemperatureUnit.Kelvin, AmountOfSubstanceUnit.Mole, LuminousIntensityUnit.Undefined)]
public void WithDefaultUnitThrowsIfSpecifiedBaseUnitsNotFullyDefined(LengthUnit length, MassUnit mass, DurationUnit time, ElectricCurrentUnit current,
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Same here, aren't we removing BaseUnits?

UnitsNet/UnitSystem.cs Outdated Show resolved Hide resolved
UnitsNet/UnitSystem.cs Show resolved Hide resolved
/// <exception cref="ArgumentException">
/// Quantity type can not be undefined.
/// </exception>
public UnitSystem WithDefaultUnit(QuantityType quantityType, UnitInfo defaultUnitInfo, BaseUnits baseUnits = null)
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BaseUnits is going away here too, right?

UnitsNet/UnitSystem.cs Outdated Show resolved Hide resolved
UnitsNet/UnitSystem.cs Outdated Show resolved Hide resolved
- renamed some tests, added comments here and there
- WithDefaultUnit : added a check for the compatibility between QuantityType and UnitInfo passed in (also added a test for this)
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lipchev commented Sep 29, 2019

Regarding all comments about BaseUnits going away- you are right- they should be going away in v5.

I just thought I might make this a two step PR (as to not make it too difficult to review)- where the first part would be the 'non-breaking' change (that allows for issue like the one described in #700 to be patched in the client code).

However, now that I think of it- I'm not sure how good a fix is to pollute one's code with something like SI_Ex (having correctly mapped all necessary defaults by hand) just to have it fixed in the next major release (and going about changing back to SI once more)...

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Regarding all comments about BaseUnits going away- you are right- they should be going away in v5.

I just thought I might make this a two step PR (as to not make it too difficult to review)- where the first part would be the 'non-breaking' change (that allows for issue like the one described in #700 to be patched in the client code).

However, now that I think of it- I'm not sure how good a fix is to pollute one's code with something like SI_Ex (having correctly mapped all necessary defaults by hand) just to have it fixed in the next major release (and going about changing back to SI once more)...

Got it, good thinking, but I suspect the PR might be easier to review if we do a clean break to begin with instead of having both old and new designs in our head at the same time. It's up to you, just do whatever you feel makes the most sense.

- added an association (1:0..1) between UnitSystem and Unit (kept the name 'BaseUnit' instead of the previously considered 'DefaultUnit')
- added an association (1:0..n) between Unit and UnitSystem- this would be used to generate list of units for a quantity in a particular unit system (not an exhaustive list, needs a review)
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lipchev commented Oct 5, 2019

Here is an example of the modified unit definition schema (haven't removed the BaseUnits from the CubicHectometer & ImperialPint as to not trigger the code-regeneration)- tell me what you think.

The two associations would be used to construct the corresponding list of UnitInfo's and default UnitInfo for a given quantity and unit system.

Modifying the whole list of UnitDefinitions in such a way would be quite the task- but as long as there is some review process- I think we can manage.

As we do that- what I think would be really cool is to associate units & quantities with their actual ontological references: like for instance our MassFraction is defined in UO as MassPercentage and again as MassFraction in OM.

We could thus (maybe in the future) run some ontological alignment validations on our unit definitions, as described in this awesome paper: Comparison and Evaluation of Ontologies for Units of Measurement.

Not to mention the nice extension methods that one could think of..

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I like it. Explicit and much simpler to reason about than before. I originally thought about defining unit system as its own file, but keeping it per quantity is actually a much better idea since it's much more visible and just a single JSON file to edit when adding new units.

It's still something new that contributors will have to think about, but with some updated steps in the wiki I think we should manage.

Also, unit systems are really opt-in the way I see it. Meaning, if we decide to not map all units they should still continue to work for everything else but methods that take a unit system as argument.

- refactored the UnitSystem- moving the BaseUnits to BaseUnitSystem (SI derived from BaseUnitSystem), extended the unit mappings with the UnitSystemInfo class (containing both default and common/derived units)
- updated the JsonTypes and created the  UnitSystemInfoGenerator (TODO WRC)
- updated existing UnitSystemTests that tested for equality/BaseUnits (almost all in fact) to use the BaseUnitSystem instead (as the IEquatble/BaseUnits interface was pushed down)
- added several more unit-system mappings to the UnitDefinitions (Acceleration, AmountOfSubstance, Area, Energy & Length)
- commented (temporary) part of the Ctor_WithValueAndSIUnitSystem_ReturnsQuantityWithSIUnitOrThrowsArgum test (testing for support SI support)
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lipchev commented Nov 12, 2019

Ok, so I refactored UnitSystem- I couldn't bear to remove the BaseUnits so I moved it the BaseUnitSystem extension of the UnitSystem (along with the IEquatable interface). It is thus still present for UnitSystem.SI (which is a BaseUnitSystem)- I don't yet know how we could is use- but I don't think it hurts to keep it for now. I've also left out the original BaseUnits constructor (and the corresponding mapping behavior)- marked as obsolete. Thus it seems we are mostly backward-compatible. (still I presume we will move this to v5?)

I've replaced the previous a UnitInfo[] mapping (in the UnitSystem) with a UnitSystemInfo- that includes the default unit (optional) and list of "common" (also "derived" or "named") units for a quantity in a unit system. This class itself is currently not exposed (maybe make internal)- only the UnitInfos are exposed via the GetDefaultUnitInfo(QuantityType quantityType) & GetCommonUnitsInfo(QuantityType quantityType) methods in the UnitSystem.

Next I updated the JSON types & added UnitSystem generator- that completes the partial part of the concrete UnitSystem implementations (SI, GGS, EE etc..) and finally added several more UnitSystem mappings to the UnitDefinitions of Acceleration, AmountOfSubstance, Area, Energy & Length (pretty much the same thing as with Volume- note however that CGS often maps default unit to prefixed-quantities).

Still some tests need to be added (note for instance how it's not really possible to argument check the Lazy in the constructor). Also I've commented(temporary) parts of the Ctor_WithValueAndSIUnitSystem_ReturnsQuantityWithSIUnitOrThrowsArgum, and two of my own tests for the WithDefaultUnit registration- that used to test for the BaseUnit- haven't created an overload for it in BaseUnitSystem yet)

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lipchev commented Nov 12, 2019

Also- the benchmark showed some unexpected results- I didn't expect to see any change over the previous tests (we are still doing the same array lookup) - yet the results turned up even faster than the original As/ToUnit methods- what, am I not doing enough argument checking somewhere? Or maybe it is something worse :)

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lipchev commented Nov 12, 2019

Method Mean Error StdDev Median Gen 0 Gen 1 Gen 2 Allocated
Constructor 9.703 ns 0.1571 ns 0.1469 ns 9.747 ns - - - -
Constructor_SI 14.399 ns 0.2823 ns 0.3138 ns 14.327 ns - - - -
FromMethod 22.979 ns 0.3424 ns 0.3036 ns 22.930 ns - - - -
ToProperty 7.132 ns 0.1730 ns 0.2188 ns 7.109 ns - - - -
As 7.117 ns 0.1795 ns 0.2631 ns 7.158 ns - - - -
As_SI 8.965 ns 0.1758 ns 0.1727 ns 8.984 ns - - - -
ToUnit 16.113 ns 0.3489 ns 0.5634 ns 16.020 ns - - - -
ToUnit_SI 19.220 ns 0.5484 ns 1.5909 ns 18.631 ns - - - -
ToStringTest 2,143.655 ns 42.0048 ns 72.4562 ns 2,124.925 ns 0.1945 - - 832 B
Parse 50,824.466 ns 1,167.4845 ns 1,674.3713 ns 50,253.683 ns 10.1929 - - 43000 B
TryParseValid 50,085.794 ns 1,109.7561 ns 1,519.0467 ns 49,460.004 ns 10.1929 - - 42976 B
TryParseInvalid 51,682.055 ns 1,388.3917 ns 1,946.3312 ns 51,121.497 ns 10.1318 - - 42576 B
QuantityFrom 64.901 ns 1.1769 ns 1.0433 ns 64.964 ns 0.0132 - - 56 B
IQuantity_As 14.626 ns 0.2431 ns 0.2274 ns 14.591 ns 0.0057 - - 24 B
IQuantity_As_SI 10.176 ns 0.1887 ns 0.1576 ns 10.154 ns - - - -
IQuantity_ToUnit 23.791 ns 0.4649 ns 0.4348 ns 23.867 ns 0.0133 - - 56 B
IQuantity_ToStringTest 1,985.983 ns 34.6024 ns 27.0153 ns 1,994.777 ns 0.1945 - - 832 B

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I've kind of forgotten to follow up on this. Will try to get to it sometime soon.

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This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

@stale stale bot added the wontfix label Feb 24, 2020
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@stale stale bot removed the wontfix label Jun 5, 2020
@angularsen angularsen added the pinned Issues that should not be auto-closed due to inactivity. label Jun 7, 2020
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angularsen commented Jun 7, 2020

I added the pinned label to prevent bot from stale-closing it.

@lipchev lipchev mentioned this pull request Jun 10, 2020
- UnitSystem/BaseUnitSystem Equality contract based on the base (default) unit for each quantity
- BaseUnits for BaseUnitSystem created from the provided unit associations
- added unit system associations for all SI base types (Length, Mass, Duration etc.)
- tests for the UnitSystem construction/derivation
in order to avoid breaking the namespace (UnitSystem.SI) all static instances were added to the UnitSystem.Definition (partial class)
- fixed typo in unit system for Length
- Ctor_UnitSystem_ThrowsArgumentExceptionIfNotSupported
- Ctor_WithNullUnitSystem_ThrowsArgumentNullException
- As_UnitSystem_ThrowsArgumentExceptionIfNotSupported
- As_WithNullUnitSystem_ThrowsArgumentNullException
- To_UnitSystem_ThrowsArgumentExceptionIfNotSupported
- ToUnit_WithNullUnitSystem_ThrowsNullException
- merged all upstream modifications
- fixed nullability issues in UnitSystem
- the Lazy<..> BaseUnits constructor was made protected
- marked all tests that rely solely on BaseUnits as Obsolete (with error=false)
- removed some obsolete tests from MassConcentration (tesing for default unit system units)
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lipchev commented Oct 6, 2020

This is almost done- still need to complete mapping in the JSON files, but as it stands I can only see one client call that is breaking : new UnitSystem(baseUnits).BaseUnits - the constructor works as before(marked as obsolete)- it is only the BaseUnits property that was moved to BaseUnitSystem- so UnitSystem.SI.BaseUnits is still valid.

I've kept the equality contract for BaseUnitSystem as before- only comparing the default SI base units, where as for all other unit systems (not derived from BaseUnitSystem) we compare all unit associations.

I've added tests akin to the ones you've suggested in #844.
There are a few more tests that can be added to UnitSystemTests (I don't think that those that I've marked as Obsolete contribute to the coverage- while the constructor they relied on is indeed obsolete- the tested behavior is still valid).

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Awesome, I'll try to take a closer look this weekend.

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@lipchev I have totally neglected this one, but stumbled over it today. Would you like me to review this still?

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Also, related #864.

Here we deprecate QuantityType in favor of strings, which is more extensible. It seems like something this PR should take into account as well.

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I would suggest the naming the alternative Unit System of "EnglishEngineering" units be defined as "USCustomary" as I believe that is the proper name. I believe the "English" or "Imperial" is historical naming and not used anymore.

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Thank you @inflectionpoint , I didn't know that!

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lipchev commented Mar 7, 2021

@angularsen I've merged everything from upstream, removing the SupportsSIUnitSystem tests in favor of the auto-generated equivalents.
There is one small thing that's been bugging me for a while- that is the Undefined unit. As far as I can tell this is only used for the SI BaseUnit definitions (where I think it could easily be replaced it with a nullable property). Do you know of any other reason for having it? Wouldn't it be better if we made BaseUnit the zero-index (default) unit for all quantities? At the very least- this would allow us to remove the nullable _unit field (well maybe not remove it, but at least make it non-nullable :)).

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@lipchev I think the reasoning for Undefined was to catch bugs where someone didn't specify a value, such as when deserializing JSON.
I'm fine with making it nullable instead since we are already making breaking changes, and I don't expect anyone to use Undefined for anything meaningful that can't be replaced with null.

…UnitSystemWithOldDerivedUnits_IncludingTheNewBaseUnit
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lipchev commented Sep 3, 2022

I don't know where to put this (maybe a discussion?) but here's a great explanation of the linear algebra behind the BaseUnits of different UnitSystems.

@angularsen angularsen modified the milestones: 5.0, vNext Feb 2, 2023
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