dotnet-core/release-notes/3.0/preview/api-diff/preview6/3.0-preview6_System.Collections.Immutable.md

System.Collections.Immutable

 namespace System.Collections.Immutable {
     public struct ImmutableArray<T> : ICollection, ICollection<T>, IEnumerable, IEnumerable<T>, IEquatable<ImmutableArray<T>>, IImmutableList<T>, IList, IList<T>, IReadOnlyCollection<T>, IReadOnlyList<T>, IStructuralComparable, IStructuralEquatable {
+        public ReadOnlyMemory<T> AsMemory();
+        public ReadOnlySpan<T> AsSpan();
     }
 }