Fix equality check for non-data classes

README.md

@@ -653,20 +653,23 @@ consistent formatting using the [`spotless`](https://github.com/diffplug/spotles
 
 ### Testing
 
-The library includes comprehensive **serialization round-trip tests** for examples published in the
+The library includes comprehensive **serialization round-trip and equality tests** for the example resources published in the
 following packages:
 
 - [hl7.fhir.r4.examples](https://simplifier.net/packages/hl7.fhir.r4.examples) (5309 examples)
 - [hl7.fhir.r4b.examples](https://simplifier.net/packages/hl7.fhir.r4b.examples) (2840 examples)
 - [hl7.fhir.r5.examples](https://simplifier.net/packages/hl7.fhir.r5.examples) (2822 examples)
 
-For each JSON example of a FHIR resource in the packages above, a test is performed with the
-following steps:
+For each JSON example of a FHIR resource in the referenced packages, two categories of tests are executed:
 
-1. Deserialization: The JSON is deserialized into the corresponding generated Kotlin resource class.
-2. Serialization: The Kotlin object is then serialized back into JSON format.
-3. Verification: The newly generated JSON is compared, character by character[^7], to the original
-   JSON to ensure complete fidelity.
+1. Serialization round-trip test:
+   - Deserialization: The JSON is parsed into its corresponding generated Kotlin resource class.
+   - Serialization: That Kotlin object is then converted back into JSON.
+   - Verification: The regenerated JSON is compared character by character[^7] with the original to confirm exact fidelity.
+2. Equality test:
+   - First instance: Deserialize the JSON into a Kotlin resource object.
+   - Second instance: Deserialize the same JSON into a separate Kotlin resource object.
+   - Verification: The two objects are structurally equal (using `==` operator).
 
 [^7]: There are several exceptions. The FHIR specification allows for some variability in data
 representation, which may lead to differences between the original and newly serialized JSON. For

fhir-codegen/gradle-plugin/src/main/kotlin/com/google/fhir/codegen/ModelTypeSpecGenerator.kt

@@ -81,6 +81,11 @@ class ModelTypeSpecGenerator(private val valueSetMap: Map<String, ValueSet>) {
             // with '_'.
             if (structureDefinition.name == "Element") {
               addModifiers(KModifier.OPEN)
+              // Implement equals/hashCode for Element to compare properties (like data classes).
+              addEqualsAndHashCodeFunctions(
+                structureDefinition.name,
+                structureDefinition.rootElements,
+              )
             } else {
               addModifiers(KModifier.SEALED)
             }
@@ -92,6 +97,12 @@ class ModelTypeSpecGenerator(private val valueSetMap: Map<String, ValueSet>) {
             // since they need to be subclassed. E.g. Uri can be extended by Url, and Quantity can
             // be extended by Duration.
             addModifiers(KModifier.OPEN)
+            // Implement equals/hashCode for open classes (to perform property-based comparison,
+            // like data classes).
+            addEqualsAndHashCodeFunctions(
+              structureDefinition.name,
+              structureDefinition.rootElements,
+            )
           } else {
             addModifiers(KModifier.DATA)
           }
@@ -195,6 +206,55 @@ class ModelTypeSpecGenerator(private val valueSetMap: Map<String, ValueSet>) {
     return typeSpec
   }
 
+  private fun TypeSpec.Builder.addEqualsAndHashCodeFunctions(
+    name: String,
+    elements: List<Element>,
+  ) {
+    if (elements.isEmpty()) return
+    val equalsFunSpec =
+      FunSpec.builder("equals")
+        .addModifiers(KModifier.OVERRIDE)
+        .addParameter("other", Any::class.asTypeName().copy(nullable = true))
+        .returns(Boolean::class)
+        .addCode(
+          """
+            if (this === other) return true
+            if (other !is ${name.capitalized()}) return false
+        """
+            .trimIndent()
+        )
+        .addCode(
+          elements.joinToString(separator = "\n", prefix = "\n", postfix = "\n") {
+            "if( ${it.getElementName()} != other.${it.getElementName()}) return false"
+          }
+        )
+        .addCode("return true")
+        .build()
+
+    this.addFunction(equalsFunSpec)
+
+    val hashCodeFunSpec =
+      FunSpec.builder("hashCode")
+        .addModifiers(KModifier.OVERRIDE)
+        .returns(Int::class)
+        .addCode(
+          "// Using 31 improves hash distribution and reduces collisions in hash-based collections\n"
+        )
+        .addCode("var result = ${elements.first().getElementName()}?.hashCode() ?: 0")
+        .addCode(
+          elements.subList(1, elements.size).joinToString(
+            separator = "\n",
+            prefix = "\n",
+            postfix = "\n",
+          ) {
+            "result = 31 * result + (${it.getElementName()}?.hashCode() ?: 0)"
+          }
+        )
+        .addCode("return result")
+        .build()
+    this.addFunction(hashCodeFunSpec)
+  }
+
   /** Adds a nested class for each BackboneElement in the [StructureDefinition]. */
   private fun TypeSpec.Builder.addBackboneElement(
     path: String,

fhir-codegen/gradle-plugin/src/main/kotlin/com/google/fhir/codegen/primitives/FhirDateFileSpecGenerator.kt

@@ -64,6 +64,7 @@ object FhirDateFileSpecGenerator {
             )
             addType(
               TypeSpec.classBuilder("YearMonth")
+                .addModifiers(KModifier.DATA)
                 .addSuperinterface(sealedInterfaceClassName)
                 .primaryConstructor(
                   FunSpec.constructorBuilder()
@@ -84,6 +85,7 @@ object FhirDateFileSpecGenerator {
             )
             addType(
               TypeSpec.classBuilder("Date")
+                .addModifiers(KModifier.DATA)
                 .addSuperinterface(sealedInterfaceClassName)
                 .primaryConstructor(
                   FunSpec.constructorBuilder().addParameter("date", LocalDate::class).build()

fhir-codegen/gradle-plugin/src/main/kotlin/com/google/fhir/codegen/primitives/FhirDateTimeFileSpecGenerator.kt

@@ -69,6 +69,7 @@ object FhirDateTimeFileSpecGenerator {
             )
             addType(
               TypeSpec.classBuilder("YearMonth")
+                .addModifiers(KModifier.DATA)
                 .addSuperinterface(sealedInterfaceClassName)
                 .primaryConstructor(
                   FunSpec.constructorBuilder()
@@ -89,6 +90,7 @@ object FhirDateTimeFileSpecGenerator {
             )
             addType(
               TypeSpec.classBuilder("Date")
+                .addModifiers(KModifier.DATA)
                 .addSuperinterface(sealedInterfaceClassName)
                 .primaryConstructor(
                   FunSpec.constructorBuilder().addParameter("date", LocalDate::class).build()
@@ -107,6 +109,7 @@ object FhirDateTimeFileSpecGenerator {
             )
             addType(
               TypeSpec.classBuilder("DateTime")
+                .addModifiers(KModifier.DATA)
                 .addSuperinterface(sealedInterfaceClassName)
                 .primaryConstructor(
                   FunSpec.constructorBuilder()

fhir-model/build.gradle.kts

@@ -134,7 +134,11 @@ kotlin {
             }
         }
         val jvmMain by getting
-        val jvmTest by getting
+        val jvmTest by getting {
+            dependencies {
+                implementation("org.jetbrains.kotlin:kotlin-reflect")
+            }
+        }
         val jsMain by getting
         val jsTest by getting
     }

fhir-model/src/commonMain/kotlin/com/google/fhir/model/r4/Element.kt

@@ -18,6 +18,9 @@
 
 package com.google.fhir.model.r4
 
+import kotlin.Any
+import kotlin.Boolean
+import kotlin.Int
 import kotlin.String
 import kotlin.Suppress
 import kotlin.collections.MutableList
@@ -44,4 +47,19 @@ public open class Element(
    * simplicity for everyone.
    */
   public open var extension: MutableList<Extension> = mutableListOf(),
-)
+) {
+  override fun equals(other: Any?): Boolean {
+    if (this === other) return true
+    if (other !is Element) return false
+    if (id != other.id) return false
+    if (extension != other.extension) return false
+    return true
+  }
+
+  override fun hashCode(): Int {
+    // Using 31 improves hash distribution and reduces collisions in hash-based collections
+    var result = id?.hashCode() ?: 0
+    result = 31 * result + (extension?.hashCode() ?: 0)
+    return result
+  }
+}

fhir-model/src/commonMain/kotlin/com/google/fhir/model/r4/FhirDate.kt

@@ -30,11 +30,11 @@ public sealed interface FhirDate {
     override fun toString(): String = value.toString()
   }
 
-  public class YearMonth(public val year: Int, public val month: Int) : FhirDate {
+  public data class YearMonth(public val year: Int, public val month: Int) : FhirDate {
     override fun toString(): String = "$year-${month.toString().padStart(2,'0')}"
   }
 
-  public class Date(public val date: LocalDate) : FhirDate {
+  public data class Date(public val date: LocalDate) : FhirDate {
     override fun toString(): String = date.toString()
   }
 

fhir-model/src/commonMain/kotlin/com/google/fhir/model/r4/FhirDateTime.kt

@@ -33,15 +33,15 @@ public sealed interface FhirDateTime {
     override fun toString(): String = value.toString()
   }
 
-  public class YearMonth(public val year: Int, public val month: Int) : FhirDateTime {
+  public data class YearMonth(public val year: Int, public val month: Int) : FhirDateTime {
     override fun toString(): String = "$year-${month.toString().padStart(2,'0')}"
   }
 
-  public class Date(public val date: LocalDate) : FhirDateTime {
+  public data class Date(public val date: LocalDate) : FhirDateTime {
     override fun toString(): String = date.toString()
   }
 
-  public class DateTime(public val dateTime: LocalDateTime, public val utcOffset: UtcOffset) :
+  public data class DateTime(public val dateTime: LocalDateTime, public val utcOffset: UtcOffset) :
     FhirDateTime {
     override fun toString(): String =
       dateTime.format(LocalDateTime.Formats.ISO) + utcOffset.toString()

fhir-model/src/commonMain/kotlin/com/google/fhir/model/r4/Integer.kt

@@ -18,6 +18,8 @@
 
 package com.google.fhir.model.r4
 
+import kotlin.Any
+import kotlin.Boolean
 import kotlin.Int
 import kotlin.String
 import kotlin.Suppress
@@ -43,6 +45,23 @@ public open class Integer(
   /** The actual value */
   public open var `value`: Int? = null,
 ) : Element(id, extension) {
+  override fun equals(other: Any?): Boolean {
+    if (this === other) return true
+    if (other !is Integer) return false
+    if (id != other.id) return false
+    if (extension != other.extension) return false
+    if (value != other.value) return false
+    return true
+  }
+
+  override fun hashCode(): Int {
+    // Using 31 improves hash distribution and reduces collisions in hash-based collections
+    var result = id?.hashCode() ?: 0
+    result = 31 * result + (extension?.hashCode() ?: 0)
+    result = 31 * result + (value?.hashCode() ?: 0)
+    return result
+  }
+
   public open fun toElement(): Element? {
     if (id != null || extension.isNotEmpty()) {
       return Element(id, extension)

fhir-model/src/commonMain/kotlin/com/google/fhir/model/r4/Quantity.kt

@@ -19,6 +19,9 @@
 package com.google.fhir.model.r4
 
 import com.google.fhir.model.r4.serializers.QuantitySerializer
+import kotlin.Any
+import kotlin.Boolean
+import kotlin.Int
 import kotlin.Suppress
 import kotlin.collections.MutableList
 import kotlinx.serialization.Serializable
@@ -74,6 +77,31 @@ public open class Quantity(
    */
   public open var code: Code? = null,
 ) : Element() {
+  override fun equals(other: Any?): Boolean {
+    if (this === other) return true
+    if (other !is Quantity) return false
+    if (id != other.id) return false
+    if (extension != other.extension) return false
+    if (value != other.value) return false
+    if (comparator != other.comparator) return false
+    if (unit != other.unit) return false
+    if (system != other.system) return false
+    if (code != other.code) return false
+    return true
+  }
+
+  override fun hashCode(): Int {
+    // Using 31 improves hash distribution and reduces collisions in hash-based collections
+    var result = id?.hashCode() ?: 0
+    result = 31 * result + (extension?.hashCode() ?: 0)
+    result = 31 * result + (value?.hashCode() ?: 0)
+    result = 31 * result + (comparator?.hashCode() ?: 0)
+    result = 31 * result + (unit?.hashCode() ?: 0)
+    result = 31 * result + (system?.hashCode() ?: 0)
+    result = 31 * result + (code?.hashCode() ?: 0)
+    return result
+  }
+
   /** How the Quantity should be understood and represented. */
   public enum class QuantityComparator(
     private val code: kotlin.String,

fhir-model/src/commonMain/kotlin/com/google/fhir/model/r4/String.kt

@@ -18,6 +18,9 @@
 
 package com.google.fhir.model.r4
 
+import kotlin.Any
+import kotlin.Boolean
+import kotlin.Int
 import kotlin.Suppress
 import kotlin.collections.MutableList
 
@@ -41,6 +44,23 @@ public open class String(
   /** The actual value */
   public open var `value`: kotlin.String? = null,
 ) : Element(id, extension) {
+  override fun equals(other: Any?): Boolean {
+    if (this === other) return true
+    if (other !is String) return false
+    if (id != other.id) return false
+    if (extension != other.extension) return false
+    if (value != other.value) return false
+    return true
+  }
+
+  override fun hashCode(): Int {
+    // Using 31 improves hash distribution and reduces collisions in hash-based collections
+    var result = id?.hashCode() ?: 0
+    result = 31 * result + (extension?.hashCode() ?: 0)
+    result = 31 * result + (value?.hashCode() ?: 0)
+    return result
+  }
+
   public open fun toElement(): Element? {
     if (id != null || extension.isNotEmpty()) {
       return Element(id, extension)

fhir-model/src/commonMain/kotlin/com/google/fhir/model/r4/Uri.kt

@@ -18,6 +18,9 @@
 
 package com.google.fhir.model.r4
 
+import kotlin.Any
+import kotlin.Boolean
+import kotlin.Int
 import kotlin.String
 import kotlin.Suppress
 import kotlin.collections.MutableList
@@ -44,6 +47,23 @@ public open class Uri(
   /** The actual value */
   public open var `value`: String? = null,
 ) : Element(id, extension) {
+  override fun equals(other: Any?): Boolean {
+    if (this === other) return true
+    if (other !is Uri) return false
+    if (id != other.id) return false
+    if (extension != other.extension) return false
+    if (value != other.value) return false
+    return true
+  }
+
+  override fun hashCode(): Int {
+    // Using 31 improves hash distribution and reduces collisions in hash-based collections
+    var result = id?.hashCode() ?: 0
+    result = 31 * result + (extension?.hashCode() ?: 0)
+    result = 31 * result + (value?.hashCode() ?: 0)
+    return result
+  }
+
   public open fun toElement(): Element? {
     if (id != null || extension.isNotEmpty()) {
       return Element(id, extension)