public static T FirstOrDefault <T>(this ReadOnlyMemory <T> memory) => memory.HasContent() ? memory.Span[0] : default;
public static T LastOrDefault <T>(this ReadOnlyMemory <T> memory) => memory.HasContent() ? memory.Span[memory.Length - 1] : default;
public static bool HasNoContent <T>(this ReadOnlyMemory <T> memory) => !memory.HasContent();