Improves and consolidates Comparator implementations (#5)

Signed-off-by: Laird Nelson <[email protected]>

Author: ljnelson

README.md

@@ -27,7 +27,7 @@ dependency:
   <groupId>org.microbean</groupId>
   <artifactId>microbean-assign</artifactId>
   <!-- Always check https://search.maven.org/artifact/org.microbean/microbean-bean for up-to-date available versions. -->
-  <version>0.0.3</version>
+  <version>0.0.4</version>
 </dependency>
 ```
 

src/main/java/org/microbean/assign/PrimitiveAndReferenceTypeKindComparator.java

@@ -0,0 +1,137 @@
+/* -*- mode: Java; c-basic-offset: 2; indent-tabs-mode: nil; coding: utf-8-unix -*-
+ *
+ * Copyright © 2025 microBean™.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+ * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+package org.microbean.assign;
+
+import java.util.Comparator;
+
+import javax.lang.model.type.TypeKind;
+
+/**
+ * A {@link Comparator} establishing a <a href="https://en.wikipedia.org/wiki/Partially_ordered_set"><dfn>partial
+ * order</dfn></a> over {@link TypeKind}s such that {@linkplain TypeKind#TYPEVAR type variables} precede {@linkplain
+ * TypeKind#isPrimitive primitive types}, {@linkplain TypeKind#isPrimitive primitive types} precede {@linkplain
+ * TypeKind#ARRAY array types}, and {@linkplain TypeKind#ARRAY array types} precede {@linkplain TypeKind#DECLARED
+ * declared types}.
+ *
+ * @author <a href="https://about.me/lairdnelson" target="_top">Laird Nelson</a>
+ *
+ * @see #compare(TypeKind, TypeKind)
+ */
+public final class PrimitiveAndReferenceTypeKindComparator implements Comparator<TypeKind> {
+
+
+  /*
+   * Static fields.
+   */
+
+
+  /**
+   * The sole instance of this class.
+   */
+  public static final PrimitiveAndReferenceTypeKindComparator INSTANCE = new PrimitiveAndReferenceTypeKindComparator();
+
+
+  /*
+   * Constructors.
+   */
+
+
+  private PrimitiveAndReferenceTypeKindComparator() {
+    super();
+  }
+
+
+  /*
+   * Instance methods.
+   */
+
+
+  /**
+   * Compares the two {@link TypeKind}s and returns the result.
+   *
+   * <p>If {@code k0} is {@code null} and {@code k1} is not, returns a positive value.</p>
+   *
+   * <p>If {@code k1} is {@code null} and {@code k0} is not, returns a negative value.</p>
+   *
+   * <p>If {@code k0} is {@link TypeKind#ARRAY}, and {@code k1} {@linkplain TypeKind#isPrimitive() is primitive},
+   * returns a positive value.</p>
+   *
+   * <p>If {@code k0} is {@link TypeKind#ARRAY}, and {@code k1} is {@link TypeKind#DECLARED}, returns a negative
+   * value.</p>
+   *
+   * <p>If {@code k0} {@linkplain TypeKind#isPrimitive() is primitive}, and {@code k1} is {@link TypeKind#ARRAY} or
+   * {@link TypeKind#DECLARED}, returns a negative value.</p>
+   *
+   * <p>If {@code k0} {@linkplain TypeKind#isPrimitive() is primitive}, and {@code k1} is {@link TypeKind#TYPEVAR},
+   * returns a positive value.</p>
+   *
+   * <p>If {@code k0} is {@link TypeKind#DECLARED}, and {@code k1} is {@link TypeKind#ARRAY}, or {@linkplain
+   * TypeKind#isPrimitive() is primitive}, or is {@link TypeKind#TYPEVAR}, returns a positive value.</p>
+   *
+   * <p>If {@code k0} is {@link TypeKind#TYPEVAR}, and {@code k1} is {@link TypeKind#ARRAY}, or {@linkplain
+   * TypeKind#isPrimitive() is primitive}, or is {@link TypeKind#DECLARED}, returns a negative value.</p>
+   *
+   * <p>Returns {@code 0} in all other cases.
+   *
+   * @param k0 a {@link TypeKind}; may be {@code null}
+   *
+   * @param k1 a {@link TypeKind}; may be {@code null}
+   *
+   * @return a comparison result
+   *
+   * @see TypeKind#isPrimitive()
+   *
+   * @see TypeKind#ARRAY
+   *
+   * @see TypeKind#DECLARED
+   *
+   * @see TypeKind#TYPEVAR
+   */
+  @Override // Comparator<TypeKind>
+  public final int compare(final TypeKind k0, final TypeKind k1) {
+    return k0 == k1 ? 0 : k0 == null ? 1 : k1 == null ? -1 : switch (k0) {
+
+    case ARRAY -> switch (k1) {
+    // Arrays come after primitives and type variables.
+    case BOOLEAN, BYTE, CHAR, DOUBLE, FLOAT, INT, LONG, SHORT, TYPEVAR -> 1;
+    // Arrays come before declared types.
+    case DECLARED -> -1; // arrays come before declared
+    default -> 0;
+    };
+
+    case BOOLEAN, BYTE, CHAR, DOUBLE, FLOAT, INT, LONG, SHORT -> switch (k1) {
+    // Primitives come before arrays and declared types.
+    case ARRAY, DECLARED -> -1;
+    // Primitives come after type variables.
+    case TYPEVAR -> 1;
+    default -> 0;
+    };
+
+    case DECLARED -> switch (k1) {
+    // Declared types come after arrays, primitives and type variables.
+    case ARRAY, BOOLEAN, BYTE, CHAR, DOUBLE, FLOAT, INT, LONG, SHORT, TYPEVAR -> 1;
+    default -> 0;
+    };
+
+    case TYPEVAR -> switch (k1) {
+      // Type variables come before arrays, primitives and declared types.
+    case ARRAY, BOOLEAN, BYTE, CHAR, DECLARED, DOUBLE, FLOAT, INT, LONG, SHORT -> -1;
+    default -> 0;
+    };
+
+    default -> 0;
+    };
+  }
+
+}

src/main/java/org/microbean/assign/PrimitiveTypesThenDeclaredTypesTypeKindComparator.java

@@ -98,7 +98,7 @@ public class Types implements Constable {
   public Types(final Domain domain) {
     super();
     this.domain = Objects.requireNonNull(domain, "domain");
-    this.c = comparing(TypeMirror::getKind, TypeVariablesFirstTypeKindComparator.INSTANCE)
+    this.c = comparing(TypeMirror::getKind, PrimitiveAndReferenceTypeKindComparator.INSTANCE)
       .thenComparing(new SpecializationComparator(domain))
       .thenComparing(Types::erasedName);
   }
@@ -279,8 +279,16 @@ public final SupertypeList supertypes(final TypeMirror t, final Predicate<? supe
     interfaceTypes.trimToSize();
     final int interfaceIndex = interfaceTypes.isEmpty() ? -1 : nonInterfaceTypes.size();
     return
-      new SupertypeList(concat(nonInterfaceTypes.stream(), // non-interface supertypes are already sorted from most-specific to least
-                               interfaceTypes.stream().sorted(this.c)) // have to sort interfaces because you can extend them in any order
+      new SupertypeList(concat(
+                               // Non-interface supertypes are already sorted from most-specific to least and will not
+                               // contain primitive types. By extension, array types will precede declared types
+                               // (java.lang.Object). If t is a type variable, then either its supertype will be another
+                               // type variable or a declared type, so type variables precede everything.
+                               nonInterfaceTypes.stream(),
+                               // Interfaces need to be explicitly sorted because they can show up in multiple
+                               // implements clauses and you want the set to be determinate.
+                               interfaceTypes.stream().sorted(this.c)
+                               )
                         .toList(),
                         interfaceIndex);
   }