Maya Modeling :: Smoothing Corners And Edges On Round Surfaces

I have been trying to figure out if there is a more efficient way of doing this for some time. It seems so basic but it always comes to play in my smoothing process.

For all you more experienced modelers, what is the best way to have the edges and corners stay at their 90 degree angles when smoothing while not compromising the roundness of the surface with artifacting or pinching in the corners. I find this problem when creating extrudes with sharp corners on curved/ round surfaces then smoothing them.