ImmutableKit.map with pre-size (#2841)

dfa1 · web-flow · commit 5cac2e3635e0 · 2022-06-08T22:22:15.000+10:00
diff --git a/src/main/java/graphql/collect/ImmutableKit.java b/src/main/java/graphql/collect/ImmutableKit.java
@@ -61,26 +61,27 @@ public static <K, V> ImmutableMap<K, V> mergeMaps(Map<K, V> m1, Map<K, V> m2) {
     }
 
     public static <T> ImmutableList<T> concatLists(List<T> l1, List<T> l2) {
-        return ImmutableList.<T>builder().addAll(l1).addAll(l2).build();
+        //noinspection UnstableApiUsage
+        return ImmutableList.<T>builderWithExpectedSize(l1.size() + l2.size()).addAll(l1).addAll(l2).build();
     }
 
     /**
      * This is more efficient than `c.stream().map().collect()` because it does not create the intermediate objects needed
      * for the flexible style.  Benchmarking has shown this to outperform `stream()`.
      *
-     * @param iterable the iterable to map
+     * @param collection the collection to map
      * @param mapper   the mapper function
      * @param <T>      for two
      * @param <R>      for result
      *
      * @return a map immutable list of results
      */
-    public static <T, R> ImmutableList<R> map(Iterable<? extends T> iterable, Function<? super T, ? extends R> mapper) {
-        assertNotNull(iterable);
+    public static <T, R> ImmutableList<R> map(Collection<? extends T> collection, Function<? super T, ? extends R> mapper) {
+        assertNotNull(collection);
         assertNotNull(mapper);
-        @SuppressWarnings("RedundantTypeArguments")
-        ImmutableList.Builder<R> builder = ImmutableList.<R>builder();
-        for (T t : iterable) {
+        @SuppressWarnings({"RedundantTypeArguments", "UnstableApiUsage"})
+        ImmutableList.Builder<R> builder = ImmutableList.<R>builderWithExpectedSize(collection.size());
+        for (T t : collection) {
             R r = mapper.apply(t);
             builder.add(r);
         }
@@ -101,6 +102,7 @@ public static <T> ImmutableList<T> addToList(Collection<? extends T> existing, T
         assertNotNull(existing);
         assertNotNull(newValue);
         int expectedSize = existing.size() + 1 + extraValues.length;
+        @SuppressWarnings("UnstableApiUsage")
         ImmutableList.Builder<T> newList = ImmutableList.builderWithExpectedSize(expectedSize);
         newList.addAll(existing);
         newList.add(newValue);
@@ -124,6 +126,7 @@ public static <T> ImmutableSet<T> addToSet(Collection<? extends T> existing, T n
         assertNotNull(existing);
         assertNotNull(newValue);
         int expectedSize = existing.size() + 1 + extraValues.length;
+        @SuppressWarnings("UnstableApiUsage")
         ImmutableSet.Builder<T> newSet = ImmutableSet.builderWithExpectedSize(expectedSize);
         newSet.addAll(existing);
         newSet.add(newValue);
diff --git a/src/test/java/benchmark/ListBenchmark.java b/src/test/java/benchmark/ListBenchmark.java
@@ -33,7 +33,7 @@ private static List<String> buildStartingList() {
         return list;
     }
 
-    Function<String, String> mapper = s -> new StringBuilder(s).reverse().toString();
+    private final Function<String, String> mapper = s -> new StringBuilder(s).reverse().toString();
 
     @Benchmark
     public void benchmarkListStream(Blackhole blackhole) {

Original file line number	Diff line number	Diff line change
`@@ -33,7 +33,7 @@ private static List<String> buildStartingList() {`
`33`	`33`	`return list;`
`34`	`34`	`}`
`35`	`35`
`36`		`- Function<String, String> mapper = s -> new StringBuilder(s).reverse().toString();`
	`36`	`+ private final Function<String, String> mapper = s -> new StringBuilder(s).reverse().toString();`
`37`	`37`
`38`	`38`	`@Benchmark`
`39`	`39`	`public void benchmarkListStream(Blackhole blackhole) {`