@stevenaw This is for discussion, to show issues we face.

Contributes to #53

I added a specific constraint for comparing strings (EqualStringConstraint)
The idea was that I then could remove the string specific modifiers (IgnoreCase, IgnoreWhiteSpace) from the actual EqualConstraint

This didn't work because the EqualConstraint modifiers, don't just apply to the type at hand, but to members of (nested) collection and dictionaries. Whether it applies is determined at runtime.

See the CollectionEqualsTests:

[TestCaseSource(nameof(IgnoreCaseData))]
public void HonorsIgnoreCase(IEnumerable expected, IEnumerable actual)
{
    Assert.That(expected, Is.EqualTo(actual).IgnoreCase);
}

The only thing this EqualsStringConstraint brings us is that this constraint doesn't allow passing in an Within constraint.
So the one test for that:

Assert.Throws<NotSupportedException>(() => Assert.That("abc", new EqualStringConstraint("abcd").Within(1)));

This no longer compiles. Hereby moving an error from runtime to compile time.

Fixes #4875