Date/Time Types - Implementing Net7 System.Numerics Types

[TheBrambleShark]

Hi all,

Maybe this is something that's already been done in .NET 9 or is on the roadmap for .NET 10, but I've run into a curious issue today with .NET 8.

I have a configuration library built on top of Microsoft.Extensions.Configuration. One of the features of this library is property validation. Here is one such method.

/// <summary>
/// Validates the provided <paramref name="entity"/> to ensure it is not null and is between
/// <paramref name="minValue"/> and <paramref name="maxValue"/>.
/// </summary>
/// <typeparam name="TNumber">The underlying numeric type.</typeparam>
/// <param name="entity">The entity to compare.</param>
/// <param name="minValue">The inclusive minimum value.</param>
/// <param name="maxValue">The exclusive maximum value.</param>
/// <param name="name">The name of the parameter to validate.</param>
protected void ValidateWithinRange<TNumber>
(
    TNumber? entity,
    TNumber? minValue = null,
    TNumber? maxValue = null,
    [CallerArgumentExpression(nameof(entity))] string? name = null)
    where TNumber : struct, IComparisonOperators<TNumber, TNumber, bool>, IMinMaxValue<TNumber>
{
    if (ValidateNotNull(entity, name))
    {
        minValue ??= TNumber.MinValue;
        maxValue ??= TNumber.MaxValue;

        if (entity >= minValue && entity.Value < maxValue)
        {
            return;
        }

        // TODO: Avoid null suppressions.
        Errors.Add(GetValueOutOfRangeError(name!, entity.ToString()!, minValue.ToString()!, maxValue.ToString()!));
    }
}

(The type param description says numeric type but this is a holdover from when I was filtering on INumber<TNumber> rather than opening it up to be more generic. The type parameter name and its documentation were not updated when this change was made.)

I would expect to be able to have a DateTime property (or any of the other date and/or time types) and validate it like so:

ValidateWithinRange(options.SomeDate, DateTime.Today.AddYears(-1), DateTime.Today.AddYears(1));

However, none of these types implement IMinMaxValue<T> or IComparisonOperators<T, T, bool>, despite all of them having MinValueandMaxValue` properties and being comparable.

I know that adding each of the relevant interfaces is a different amount of work for each interface, but I did want to at least start discussion on which interfaces are worth implementing here and what the challenges would be.

---

Correction: I stated they all have MinValue and MaxValue properties, though this isn't exactly correct.

DateTime, DateTimeOffset, and TimeSpan have MinValue and MaxValue fields. This may cause issues because converting fields to properties is a binary breaking change and we can't just add properties in tandem because of the name collision issue.

DateOnly and TimeOnly have MinValue and MaxValue properties, so in theory we might only need to add the interface and that should be done.

[stephentoub]

cc: @tannergooding

[tannergooding]

Same as with other similar issues.

I had proposed these types include such interfaces in the initial design and API review rejected it at the time pending user scenarios being provided and further discussion around what it would mean for .NET as a whole.

Such built-in types cannot be updated in already shipped versions (.NET 7/8/9). It could be updated in a future version (.NET 10/11/etc) but needs to go through API review for approval first.

[TheBrambleShark]

I feel .NET 10 may be a tight squeeze for some of these features, but do you think I should create a proper API proposal for these types or does this warrant more discussion first?

At the very least, if you could share what interfaces you were thinking would be good to add, I can start working on the API proposal for adding those and exactly what that would look like. Just not sure entirely how we'd want to split this up (one omnibus proposal vs one proposal per type/interface).