AutoCAD's Dirty Little Secret

When you starting out programming in AutoCAD occasionally people mention this mysterious object called a Curve, more specifically the AcDbCurve object. The Curve object is the base class that other objects are built on such as AcDb2dPolyline, AcDb3dPolyline, AcDbArc, AcDbCircle, AcDbEllipse, AcDbLeader, AcDbLine, AcDbPolyline, AcDbRay, AcDbSpline, and AcDbXline. Additionally Civil 3D objects are also built on top of the Curve such as Alignments, FeatureLines, Pipes and Profiles.

You can get information from a curve instance of the object instead of the type of object in the drawing. For instance if you want to get information from both a Polyline and a FeatureLine you can get the objects as a Curve instead and not worry about handling both objects separately.