This .NET class wraps the AcDbXline ObjectARX class. 

The Xline class represents the XLINE entity type within AutoCAD. An xline entity is a line that extends to infinity in both directions.

Autodesk.AutoCAD.DatabaseServices.DBObject
    Autodesk.AutoCAD.DatabaseServices.Entity
        Autodesk.AutoCAD.DatabaseServices.Curve
            Autodesk.AutoCAD.DatabaseServices.Xline

Public Class Xline
Inherits Curve

public class Xline : Curve;