Given and Using

In simple words#

Learning objectives#

• Define given instances
• Write methods with using parameters
• Build a simple type class
• Use built-in Ordering givens

Explanation#

given Ordering[Product] = Ordering.by(_.price) provides an ordering wherever one is needed.

def show[A](a: A)(using s: Show[A]) asks the compiler to find a Show[A].

Type classes add behaviour to types you don’t own (Int, String, third-party classes).

Givens are imported explicitly with import mypackage.given — this replaces Scala 2’s implicit.

Code example: A Show type class#

1trait Show[A]:
2  def show(a: A): String
3

4case class Product(name: String, price: Double)
5

6given Show[Int] with
7  def show(n: Int) = s"#$n"
8

9given Show[Product] with
10  def show(p: Product) = f"${p.name} (₹${p.price}%,.0f)"
11

12def printAll[A](items: List[A])(using s: Show[A]): Unit =
13  items.foreach(i => println(s.show(i)))
14

15given Ordering[Product] = Ordering.by(_.price)
16

17val products = List(Product("Laptop", 55000), Product("Mouse", 1400))
18printAll(List(1, 2))
19printAll(products.sorted)     // sorted uses the given Ordering

#1
#2
Mouse (₹1,400)
Laptop (₹55,000)

This example is illustrative. Copy or download it and run it in your own environment; the expected output is shown above.

Step-by-step explanation#

1. Show[A] is a type class.
2. given instances define Show for Int and Product.
3. printAll asks for a Show[A] with using.
4. sorted finds the given Ordering[Product].

Real-world use case#

Common mistakes#

Best practices#

• Use for type classes and context
• Put givens in companion objects
• Import givens explicitly
• Avoid ambiguity

Remember this#

Practice exercise#

1given Ordering[String] = Ordering.by(_.length)
2List("Scala", "Go", "Java").sorted  // List(Go, Java, Scala)

Mini quiz#

Want more? Practise all Scala MCQs · Scala interview questions

Related topics#

My notes#

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