Ambiguous call for ToHashSet

[thomaslevesque]

Linq.Extras has a ToHashSet method, but an identical method was introduced in Linq in the following TFMs:

• .NET Framework 4.7.2
• .NET Core 2.0
• .NET Standard 2.1

This causes an ambiguity when both the System.Linq and Linq.Extras namespaces are imported.

New targets should be added that exclude this method:

  netstandard1.0
  netstandard1.6
  netstandard2.0
+ netstandard2.1
  net45
  net471
+ net472
+ netcoreapp2.0

[thomaslevesque]

Interestingly, source.ToHashSet(comparer) is ambiguous, but source.ToHashSet() is not.
This is because Linq actually has two distinct overloads (one with the comparer parameter, one without), whereas Linq.Extras has only one, with an optional comparer parameter.
If the comparer is not specified, the compiler selects the overload without the comparer parameter over the one with an optional comparer parameter.