ChatGPT generated. Working. Scala macro for entities custom comparison logic + Analogs without Macro

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Scala Macro for Custom Entity Comparison

This gist contains a Scala 3 macro that compares two entities field by field, automatically skipping any fields where exactly one of the values is null. The comparison logic is generated at compile time using Scala's quoted API, which ensures no runtime reflection overhead.

Features

• Compare two entities of any type.
• Skip fields with null values based on predefined business rules.
• Avoid runtime reflection by generating code at compile time.

Example

The example compares two Address objects:

@main def main(): Unit = {
  val testCases = List(
    (("USA", null, "New York"), ("USA", "NY", null)),                  // true
    ((null, null, null), (null, null, null)),                          // true
    (("USA", null, null), ("USA", null, null)),                        // true
    (("Germany", "Berlin", "Berlin"), ("Germany", "Berlin", null)),    // true
    (("France", "Paris", "Lyon"), ("France", "Paris", "Lyon")),        // true
    (("Canada", null, "Toronto"), ("Canada", "Ontario", "Toronto")),   // true
    ((null, "California", null), (null, "California", "Los Angeles")), // true
    (("Italy", "Rome", null), ("Italy", null, "Rome")),                // true
    (("Japan", "Tokyo", "Shibuya"), ("Japan", "Kyoto", "Osaka")),      // false
    (("Poland", null, "New York"), ("USA", "NY", null)),               // false
  )

  testCases.foreach { case (a, b) =>
    val addrA = Address(a._1, a._2, a._3)
    val addrB = Address(b._1, b._2, b._3)
    println(compareEntity(addrA, addrB))
  }
}

case class Address(country: String, state: String, city: String)

AAA. MacroDef.scala

import scala.quoted.*

inline def compareEntity[T](a: T, b: T): Boolean =
  ${compareEntitiesImpl('a, 'b)}

def compareEntitiesImpl[T: Type](a: Expr[T], b: Expr[T])(using Quotes): Expr[Boolean] = {
  import quotes.reflect.*

  val tpe = TypeRepr.of[T]
  val fields = tpe.typeSymbol.caseFields

  val comparisons = fields.map { field =>
    val fieldName = field.name
    val aField = Select(a.asTerm, field)
    val bField = Select(b.asTerm, field)

    '{
      val aVal = ${aField.asExpr}
      val bVal = ${bField.asExpr}
      aVal == bVal || aVal == null || bVal == null
    }
  }

  comparisons.reduceLeft((acc, next) => '{ $acc && $next })
}

Analog. Without Macro. Mirror.ProductOf[A].scala

@main def main(): Unit = {
  val testCases = List(
    (("USA", null, "New York"), ("USA", "NY", null)), // true
    ((null, null, null), (null, null, null)), // true
    (("USA", null, null), ("USA", null, null)), // true
    (("Germany", "Berlin", "Berlin"), ("Germany", "Berlin", null)), // true
    (("France", "Paris", "Lyon"), ("France", "Paris", "Lyon")), // true
    (("Canada", null, "Toronto"), ("Canada", "Ontario", "Toronto")), // true
    ((null, "California", null), (null, "California", "Los Angeles")), // true
    (("Italy", "Rome", null), ("Italy", null, "Rome")), // true
    (("Japan", "Tokyo", "Shibuya"), ("Japan", "Kyoto", "Osaka")), // false
    (("Poland", null, "New York"), ("USA", "NY", null)), // false
  )

  testCases.foreach { case (a, b) =>
    val addrA = Address(a._1, a._2, a._3)
    val addrB = Address(b._1, b._2, b._3)
    println(compareProduct(addrA, addrB))
  }
}

def compareProduct[A](a: A, b: A)(using m: Mirror.ProductOf[A]): Boolean = {
  a.asInstanceOf[Product].productIterator.zip(b.asInstanceOf[Product].productIterator).forall {
    case (aVal, bVal) => aVal == bVal || aVal == null || bVal == null
  }
}

Analog. Without Macro. Using `productIterator`.scala

case class Address(country: String, state: String, city: String)

@main def main(): Unit = {
  val testCases = List(
    (("USA", null, "New York"), ("USA", "NY", null)), // true
    ((null, null, null), (null, null, null)), // true
    (("USA", null, null), ("USA", null, null)), // true
    (("Germany", "Berlin", "Berlin"), ("Germany", "Berlin", null)), // true
    (("France", "Paris", "Lyon"), ("France", "Paris", "Lyon")), // true
    (("Canada", null, "Toronto"), ("Canada", "Ontario", "Toronto")), // true
    ((null, "California", null), (null, "California", "Los Angeles")), // true
    (("Italy", "Rome", null), ("Italy", null, "Rome")), // true
    (("Japan", "Tokyo", "Shibuya"), ("Japan", "Kyoto", "Osaka")), // false
    (("Poland", null, "New York"), ("USA", "NY", null)), // false
  )

  testCases.foreach { case (a, b) =>
    val addrA = Address(a._1, a._2, a._3)
    val addrB = Address(b._1, b._2, b._3)
    println(compareProduct(addrA, addrB))
  }
}

def compareProduct(a: Product, b: Product): Boolean = {
  a.productIterator.zip(b.productIterator).forall {
    case (aVal, bVal) => aVal == bVal || aVal == null || bVal == null
  }
}