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Avoid iterating multiple times in uniqueIndex for collections that might be filtered on the fly. #8201

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Merged
copybara-service merged 1 commit into from
Feb 5, 2026
+14 −2
Merged

Avoid iterating multiple times in uniqueIndex for collections that might be filtered on the fly. #8201

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8 changes: 7 additions & 1 deletion android/guava/src/com/google/common/collect/Maps.java
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,7 @@
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NavigableMap;
Expand Down Expand Up @@ -1290,7 +1291,12 @@ public static <K, V> ImmutableMap<K, V> toMap(
@CanIgnoreReturnValue
public static <K, V> ImmutableMap<K, V> uniqueIndex(
Iterable<V> values, Function<? super V, K> keyFunction) {
if (values instanceof Collection) {
// We can provide a hint to the builder to preallocate the correct size when the iterable is
// either a List (which likely has a fast size() implementation), or an ImmutableCollection
// (which definitely has a fast size() implementation). While Collection also has a size()
// implementation, it _may_ require iteration over the entire collection (e.g., a
// FilteredCollection), which we want to avoid.
if (values instanceof List || values instanceof ImmutableCollection) {
return uniqueIndex(
values.iterator(),
keyFunction,
Expand Down
8 changes: 7 additions & 1 deletion guava/src/com/google/common/collect/Maps.java
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,7 @@
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NavigableMap;
Expand Down Expand Up @@ -1324,7 +1325,12 @@ public static <K, V> ImmutableMap<K, V> toMap(
@CanIgnoreReturnValue
public static <K, V> ImmutableMap<K, V> uniqueIndex(
Iterable<V> values, Function<? super V, K> keyFunction) {
if (values instanceof Collection) {
// We can provide a hint to the builder to preallocate the correct size when the iterable is
// either a List (which likely has a fast size() implementation), or an ImmutableCollection
// (which definitely has a fast size() implementation). While Collection also has a size()
// implementation, it _may_ require iteration over the entire collection (e.g., a
// FilteredCollection), which we want to avoid.
if (values instanceof List || values instanceof ImmutableCollection) {
return uniqueIndex(
values.iterator(),
keyFunction,
Expand Down
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