In a large mixing bowl, combine fruit, sugar, tapioca, and salt. Let the mixture sit while you prepare your pastry. If you used frozen fruit, let the mixture sit until it is at least partially thawed and the sugar has begun to dissolve into juices.
Roll out pastry for bottom pie crust, place it in a 9-inch pie plate, and trim the edges.
Transfer fruit mixture into bottom crust in pie plate. Dot with butter.
Roll out top crust and place it over the fruit. Trim and seal the edges. Poke a few holes in the top crust for ventilation.
Bake for 50 minutes or until crust is browned and centre is bubbly.