louthy/language-ext · error · ArgumentException

must be of type Time

Error message

must be of type Time

What it means

Time's explicit IComparable.CompareTo(object?) throws ArgumentException('must be of type Time') when passed a non-null object that is not a Time. This is the standard non-generic IComparable contract: null compares as 'greater than nothing' (returns 1), same type delegates to CompareTo(Time), anything else is rejected. The non-generic overload is only reached through APIs typed as object or IComparable.

Solutions

1. Ensure all compared values are Time instances before non-generic comparison
2. Prefer the generic IComparable<Time>/sort overloads (List<Time>.Sort) so type mismatches cannot occur
3. Check `obj is Time` before calling the non-generic CompareTo
4. Catch ArgumentException only at legacy-collection boundaries

Example fix

// before
object[] xs = { new Time(1), new TimeSq(2) };
Array.Sort(xs); // ArgumentException: must be of type Time
// after
var xs2 = new List<Time> { new Time(1), new Time(2) };
xs2.Sort();

if (obj is not Time) throw new ArgumentException($"expected Time, got {obj?.GetType().Name}");

static bool IsTime(object? o) => o is Time;

try { r = ((IComparable)time).CompareTo(obj); }
catch (ArgumentException) { r = -1; /* or handle type mismatch explicitly */ }

When it happens

Trigger: Passing a non-Time object (boxed value, different unit type like Velocity, string) to a non-generic sort/compare path such as ArrayList.BinarySearch, Array.Sort(object[]), or CompareTo((object)other) where the value is not a Time.

Common situations: Mixing unit types in legacy non-generic collections; reflection-based comparison code; sorting heterogeneous object arrays that were assumed homogeneous; refactor that changed an element type without updating non-generic sort calls.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• must be of type TimeSq
• must be of type Velocity
• must be of type VelocitySq
• The minimum value for
• Ord attribute should have a struct type that derives from…

AI-assisted analysis of louthy/language-ext@2f0e362824 (2026-09-15). Data as JSON: /api/errors/c1234c2c88b35725. Report an issue: GitHub.

Appendix: source

Thrown at LanguageExt.Core/Units of Measure/Time.cs:45

    public bool Equals(Time other) =>
        Value.Equals(other.Value);

    public bool Equals(Time other, double epsilon) =>
        Math.Abs(other.Value - Value) < epsilon;

    public override bool Equals(object? obj) =>
        obj is Time time && Equals(time);

    public override int GetHashCode() =>
        Value.GetHashCode();

    public int CompareTo(object? obj) =>
        obj switch
        {
            null       => 1,
            Time other => CompareTo(other),
            _          => throw new ArgumentException($"must be of type {nameof(Time)}")
        };

    public int CompareTo(Time other) =>
        Value.CompareTo(other.Value);

    public Time Add(Time rhs) =>
        new (Value + rhs.Value);

    public Time Subtract(Time rhs) =>
        new (Value - rhs.Value);

    public Time Multiply(double rhs) =>
        new (Value * rhs);

    public Time Divide(double rhs) =>
        new (Value / rhs);

    public static Time operator *(Time lhs, double rhs) =>

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