From a5efba94514c5466bcb1c74891f624aa0482d43b Mon Sep 17 00:00:00 2001
From: Miles Ziemer <mziemer@amazon.com>
Date: Wed, 24 May 2023 11:39:17 -0400
Subject: [PATCH] Use array to return required members

---
 .../smithy/model/shapes/CollectionShape.java  |  4 +--
 .../amazon/smithy/model/shapes/MapShape.java  |  6 ++--
 .../amazon/smithy/model/shapes/Shape.java     | 33 +++++++++----------
 3 files changed, 20 insertions(+), 23 deletions(-)

diff --git a/smithy-model/src/main/java/software/amazon/smithy/model/shapes/CollectionShape.java b/smithy-model/src/main/java/software/amazon/smithy/model/shapes/CollectionShape.java
index 06d248ce981..5d88c25573b 100644
--- a/smithy-model/src/main/java/software/amazon/smithy/model/shapes/CollectionShape.java
+++ b/smithy-model/src/main/java/software/amazon/smithy/model/shapes/CollectionShape.java
@@ -36,8 +36,8 @@ public abstract class CollectionShape extends Shape {
 
     CollectionShape(Builder<?, ?> builder) {
         super(builder, false);
-        Map<String, MemberShape> members = getRequiredMembers(builder, "member");
-        member = members.get("member");
+        MemberShape[] members = getRequiredMembers(builder, "member");
+        member = members[0];
         validateMemberShapeIds();
     }
 
diff --git a/smithy-model/src/main/java/software/amazon/smithy/model/shapes/MapShape.java b/smithy-model/src/main/java/software/amazon/smithy/model/shapes/MapShape.java
index ad975d6dd36..cab5ed6a800 100644
--- a/smithy-model/src/main/java/software/amazon/smithy/model/shapes/MapShape.java
+++ b/smithy-model/src/main/java/software/amazon/smithy/model/shapes/MapShape.java
@@ -43,9 +43,9 @@ public final class MapShape extends Shape implements ToSmithyBuilder<MapShape> {
 
     private MapShape(Builder builder) {
         super(builder, false);
-        Map<String, MemberShape> members = getRequiredMembers(builder, "key", "value");
-        key = members.get("key");
-        value = members.get("value");
+        MemberShape[] members = getRequiredMembers(builder, "key", "value");
+        key = members[0];
+        value = members[1];
         validateMemberShapeIds();
     }
 
diff --git a/smithy-model/src/main/java/software/amazon/smithy/model/shapes/Shape.java b/smithy-model/src/main/java/software/amazon/smithy/model/shapes/Shape.java
index 60ced14f2cc..847501cb888 100644
--- a/smithy-model/src/main/java/software/amazon/smithy/model/shapes/Shape.java
+++ b/smithy-model/src/main/java/software/amazon/smithy/model/shapes/Shape.java
@@ -109,18 +109,18 @@ protected void validateMixins(Map<ShapeId, Shape> mixins, Map<ShapeId, Trait> in
         }
     }
 
-    protected Map<String, MemberShape> getRequiredMembers(
-            AbstractShapeBuilder<?, ?> builder,
-            String... requiredMembersNames
-    ) {
+    protected MemberShape[] getRequiredMembers(AbstractShapeBuilder<?, ?> builder, String... requiredMembersNames) {
         // Only lists/sets and maps have required members, the maximum number being 2.
         List<String> missingMembersNames = new ArrayList<>(2);
-        Map<String, MemberShape> members = new HashMap<>(2);
 
-        for (String requiredMemberName : requiredMembersNames) {
-            Optional<MemberShape> member = getRequiredMixinMember(builder, requiredMemberName);
-            if (member.isPresent()) {
-                members.put(requiredMemberName, member.get());
+        // Caller knows the order of provided member names, so we don't need a dynamic data structure.
+        MemberShape[] members = new MemberShape[requiredMembersNames.length];
+
+        for (int memberNameIndex = 0; memberNameIndex < requiredMembersNames.length; memberNameIndex++) {
+            String requiredMemberName = requiredMembersNames[memberNameIndex];
+            MemberShape member = getRequiredMixinMember(builder, requiredMemberName);
+            if (member != null) {
+                members[memberNameIndex] = member;
             } else {
                 missingMembersNames.add(requiredMemberName);
             }
@@ -133,13 +133,10 @@ protected Map<String, MemberShape> getRequiredMembers(
         return members;
     }
 
-    protected Optional<MemberShape> getRequiredMixinMember(
-            AbstractShapeBuilder<?, ?> builder,
-            String requiredMemberName
-    ) {
+    private MemberShape getRequiredMixinMember(AbstractShapeBuilder<?, ?> builder, String requiredMemberName) {
         Optional<MemberShape> memberOnBuilder = builder.getMember(requiredMemberName);
         if (memberOnBuilder.isPresent()) {
-            return memberOnBuilder;
+            return memberOnBuilder.get();
         }
 
         // Get the most recently introduced mixin member with the given name.
@@ -155,18 +152,18 @@ protected Optional<MemberShape> getRequiredMixinMember(
         }
 
         if (mostRecentMember == null) {
-            return Optional.empty();
+            return null;
         }
 
-        return Optional.of(MemberShape.builder()
+        return MemberShape.builder()
                 .id(getId().withMember(requiredMemberName))
                 .target(mostRecentMember.getTarget())
                 .source(getSourceLocation())
                 .addMixin(mostRecentMember)
-                .build());
+                .build();
     }
 
-    protected SourceException missingRequiredMembersException(List<String> missingMembersNames) {
+    private SourceException missingRequiredMembersException(List<String> missingMembersNames) {
         String missingRequired = missingMembersNames.size() > 1 ? "members" : "member";
         String missingMembers = String.join(", ", missingMembersNames);
         String message = String.format("Missing required %s of shape `%s`: %s",