Added Value (variant) Type

[KrzysztofCwalina]

From time to time we run into cases where we want to store a heterogenous collection of values. This type allows to store such values while minimizing boxing. The type was developed by @JeremyKuhne. The original idea was that this type ends up in the BCL, but the idea was rejected.

Here is an example of a very similar type in a track2 library: https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/timeseriesinsights/Azure.IoT.TimeSeriesInsights/src/Models/TimeSeriesValue.cs

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[annelo-msft]

From time to time we run into cases where we want to store a heterogenous collection of values.

Is there a sample showing how we would use it this way in an Azure SDK context?

[KrzysztofCwalina]

@annelo-msft, this is how it's used today in one of the track 2 libraries: https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/timeseriesinsights/Azure.IoT.TimeSeriesInsights/src/Models/TimeSeriesValue.cs

[annelo-msft]

Might make sense to add a few docstrings for key APIs on Value. Also, I defer to you on whether we have concerns about calls to Unsafe.

[JeremyKuhne]

FYI: I remembered why I didn't store Type for null values. It does, of course, make it more performant. The key reason was I wanted to keep the semantics the same as casting to/from object. You could support storing the passed in Type information, but it would add non-trivial performance and cognitive overhead.

Possible options when you need to store a given type with no value:

• Store the Type object itself
• Use an enum that represents this `public enum NullOfType { SomeTypeName }