Feature: Refine distance calculation and improve exception messages in RangeData

Author: Mykyta Zotov

src/Domain/Intervals.NET.Domain.Extensions/Variable/RangeDomainExtensions.cs

@@ -122,7 +122,9 @@ public static RangeValue<double> Span<TRangeValue, TDomain>(this Range<TRangeVal
                 return HandleSingleStepCase(range, domain);
         }
 
-        var distance = domain.Distance(firstStep, lastStep);
+        // Note: IRangeDomain.Distance returns long, but for variable-step domains we interpret
+        // this as the number of complete steps and add 1.0 to get the span including boundaries
+        var distance = (double)domain.Distance(firstStep, lastStep);
         return distance + 1.0;
 
         // Local functions

src/Intervals.NET.Data/Extensions/RangeDataExtensions.cs

@@ -53,7 +53,7 @@ private static void ValidateDomainEquality<TRangeType, TDataType, TRangeDomain>(
         where TRangeType : IComparable<TRangeType>
         where TRangeDomain : IRangeDomain<TRangeType>
     {
-        if (!left.Domain.Equals(right.Domain))
+        if (!EqualityComparer<TRangeDomain>.Default.Equals(left.Domain, right.Domain))
         {
             throw new ArgumentException(
                 $"Cannot {operationName} RangeData objects with different domain instances. " +

src/Intervals.NET.Data/RangeData.cs

@@ -73,11 +73,12 @@ public RangeData(Range<TRangeType> range, IEnumerable<TDataType> data, TRangeDom
     /// The point within the range for which to retrieve the data element.
     /// </param>
     /// <exception cref="IndexOutOfRangeException">
-    /// Thrown if the calculated index is outside the bounds of the data collection.
+    /// Thrown if no data element is available for the specified point, for example because the point is
+    /// outside the range or the underlying data sequence does not provide a value for that point.
     /// </exception>
     public TDataType this[TRangeType point] => TryGet(point, out var data)
         ? data!
-        : throw new IndexOutOfRangeException($"The point {point} is outside the bounds of the range data.");
+        : throw new IndexOutOfRangeException($"No data element is available for point {point} in this RangeData (point may be outside the range or the underlying data sequence may be too short).");
 
     /// <summary>
     /// Gets the data elements corresponding to the specified sub-range within the range,

tests/Intervals.NET.Data.Tests/RangeDataTests.cs

@@ -166,11 +166,6 @@ public void SubRangeIndexer_OpenRange_EmptyRange_ReturnsEmpty()
     [Fact]
     public void SubRangeIndexer_OpenRange_SinglePointRange_ThrowsArgumentException()
     {
-        // Arrange
-        var range = Range.Closed<int>(0, 10);
-        var data = new[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
-        var rangeData = new RangeData<int, int, IntegerFixedStepDomain>(range, data, _domain);
-
         // Act - Get (5, 5) → should throw because (5, 5) is invalid (start == end with both exclusive)
         var exception = Record.Exception(() => Range.Open(5, 5));