case class equality: Making scala only check some params, not all

CaseClassEquality.scala

case class Product(name: String)(val price: Double)

// we can choose to only supply the name, i.e. partially applied
val banana=Product("banana") _

val banana10=banana(10)
val bananafree=banana(0)
val apple=Product("apple")(5)

val list=List(banana10, apple, bananafree)

// Note, price is not used for equality, but is still very much present
list.filter(_==banana10).map(_.price)
list.filter(_==bananafree).map(_.price)
list.filter(_==apple).map(_.price)

output.txt

list: List[Product] = List(Product(banana), Product(apple), Product(banana))

res1: List[Double] = List(10.0, 0.0)
res2: List[Double] = List(10.0, 0.0)
res3: List[Double] = List(5.0)