Type-safe Equal

Type-safe Equal

== in Scala is not type safe so the following code can never be true as their types are different but it has no compile-time error.

1 == "1" // always false, no compile-time error

just-fp has Equal typeclass with typeclass instances for value types (Byte, Short, Int, Char, Long, Float and Double) as well as String, BigInt and BigDecimal.

It also has Equal typeclass instances for WriterT, Writer and EitherT.

With just-fp,

import just.fp.syntax._
// use triple equals from just-fp
1 === "1"
// error: type mismatch;
// found : String("1")
// required: Int
1 === 1
// res1: Boolean = true
"a" === "a"
// res2: Boolean = true
1 !== 1
// res3: Boolean = false
1 !== 2
// res4: Boolean = true

If it's a case class the equals of which can be used for equality check, NatualEqual can be used.

e.g.)

final case class Foo(n: Int)
Foo(1) === Foo(1)
// error: value === is not a member of repl.Session.App0.Foo
// object Foo {
// ^

This can be solved by NatualEqual.equalA[A].

import just.fp._, syntax._
final case class Foo(n: Int)
object Foo {
implicit val eqaul: Equal[Foo] = Equal.equalA[Foo]
}
Foo(1) === Foo(1)
// res8: Boolean = true
// Boolean = true
Foo(1) === Foo(2)
// res9: Boolean = false
// Boolean = false
Foo(1) !== Foo(1)
// res10: Boolean = false
// Boolean = false
Foo(1) !== Foo(2)
// res11: Boolean = true