From 75110e936dcc50a75df10ffab260d30a073bf00e Mon Sep 17 00:00:00 2001
From: cpovirk <cpovirk@google.com>
Date: Fri, 14 May 2021 03:46:11 -0700
Subject: [PATCH] Generalize `Function` and `Predicate` factories to let
 callers specify the desired input type.

RELNOTES=`base`: Changed `Functions.forSupplier` and `Predicates.instanceOf` to accept an additional type argument to specify the input type for the returned `Function`/`Predicate`. The flexibility we're adding should typically not be necessary if users follow the [PECS](https://stackoverflow.com/a/2723538/28465) principle, but it can be useful in some cases, particularly around nullness analysis. Note that this change may require updates to callers' source code (to specify an additional type argument). Still, it maintains _binary_ compatibility.
PiperOrigin-RevId: 373757473
---
 .../guava/src/com/google/common/base/Functions.java    | 10 +++++-----
 .../guava/src/com/google/common/base/Predicates.java   | 10 +++++-----
 guava/src/com/google/common/base/Functions.java        | 10 +++++-----
 guava/src/com/google/common/base/Predicates.java       | 10 +++++-----
 4 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/android/guava/src/com/google/common/base/Functions.java b/android/guava/src/com/google/common/base/Functions.java
index 805f15c73727..8c8e1d5cb3a6 100644
--- a/android/guava/src/com/google/common/base/Functions.java
+++ b/android/guava/src/com/google/common/base/Functions.java
@@ -361,12 +361,12 @@ public String toString() {
    *
    * @since 10.0
    */
-  public static <T> Function<Object, T> forSupplier(Supplier<T> supplier) {
-    return new SupplierFunction<T>(supplier);
+  public static <F, T> Function<F, T> forSupplier(Supplier<T> supplier) {
+    return new SupplierFunction<>(supplier);
   }
 
   /** @see Functions#forSupplier */
-  private static class SupplierFunction<T> implements Function<Object, T>, Serializable {
+  private static class SupplierFunction<F, T> implements Function<F, T>, Serializable {
 
     private final Supplier<T> supplier;
 
@@ -375,14 +375,14 @@ private SupplierFunction(Supplier<T> supplier) {
     }
 
     @Override
-    public T apply(@NullableDecl Object input) {
+    public T apply(@NullableDecl F input) {
       return supplier.get();
     }
 
     @Override
     public boolean equals(@NullableDecl Object obj) {
       if (obj instanceof SupplierFunction) {
-        SupplierFunction<?> that = (SupplierFunction<?>) obj;
+        SupplierFunction<?, ?> that = (SupplierFunction<?, ?>) obj;
         return this.supplier.equals(that.supplier);
       }
       return false;
diff --git a/android/guava/src/com/google/common/base/Predicates.java b/android/guava/src/com/google/common/base/Predicates.java
index 9c8f1e5ea256..75d95fdfedec 100644
--- a/android/guava/src/com/google/common/base/Predicates.java
+++ b/android/guava/src/com/google/common/base/Predicates.java
@@ -169,8 +169,8 @@ public static <T> Predicate<T> equalTo(@NullableDecl T target) {
    * instances {@code Lists.newArrayList(1)} and {@code Arrays.asList(1)}.
    */
   @GwtIncompatible // Class.isInstance
-  public static Predicate<Object> instanceOf(Class<?> clazz) {
-    return new InstanceOfPredicate(clazz);
+  public static <T> Predicate<T> instanceOf(Class<?> clazz) {
+    return new InstanceOfPredicate<T>(clazz);
   }
 
   /**
@@ -472,7 +472,7 @@ public String toString() {
 
   /** @see Predicates#instanceOf(Class) */
   @GwtIncompatible // Class.isInstance
-  private static class InstanceOfPredicate implements Predicate<Object>, Serializable {
+  private static class InstanceOfPredicate<T> implements Predicate<T>, Serializable {
     private final Class<?> clazz;
 
     private InstanceOfPredicate(Class<?> clazz) {
@@ -480,7 +480,7 @@ private InstanceOfPredicate(Class<?> clazz) {
     }
 
     @Override
-    public boolean apply(@NullableDecl Object o) {
+    public boolean apply(@NullableDecl T o) {
       return clazz.isInstance(o);
     }
 
@@ -492,7 +492,7 @@ public int hashCode() {
     @Override
     public boolean equals(@NullableDecl Object obj) {
       if (obj instanceof InstanceOfPredicate) {
-        InstanceOfPredicate that = (InstanceOfPredicate) obj;
+        InstanceOfPredicate<?> that = (InstanceOfPredicate<?>) obj;
         return clazz == that.clazz;
       }
       return false;
diff --git a/guava/src/com/google/common/base/Functions.java b/guava/src/com/google/common/base/Functions.java
index be845c6a45ff..351813bba885 100644
--- a/guava/src/com/google/common/base/Functions.java
+++ b/guava/src/com/google/common/base/Functions.java
@@ -359,12 +359,12 @@ public String toString() {
    *
    * @since 10.0
    */
-  public static <T> Function<Object, T> forSupplier(Supplier<T> supplier) {
-    return new SupplierFunction<T>(supplier);
+  public static <F, T> Function<F, T> forSupplier(Supplier<T> supplier) {
+    return new SupplierFunction<>(supplier);
   }
 
   /** @see Functions#forSupplier */
-  private static class SupplierFunction<T> implements Function<Object, T>, Serializable {
+  private static class SupplierFunction<F, T> implements Function<F, T>, Serializable {
 
     private final Supplier<T> supplier;
 
@@ -373,14 +373,14 @@ private SupplierFunction(Supplier<T> supplier) {
     }
 
     @Override
-    public T apply(@Nullable Object input) {
+    public T apply(@Nullable F input) {
       return supplier.get();
     }
 
     @Override
     public boolean equals(@Nullable Object obj) {
       if (obj instanceof SupplierFunction) {
-        SupplierFunction<?> that = (SupplierFunction<?>) obj;
+        SupplierFunction<?, ?> that = (SupplierFunction<?, ?>) obj;
         return this.supplier.equals(that.supplier);
       }
       return false;
diff --git a/guava/src/com/google/common/base/Predicates.java b/guava/src/com/google/common/base/Predicates.java
index 033ab6c26c37..3fd950bc20ee 100644
--- a/guava/src/com/google/common/base/Predicates.java
+++ b/guava/src/com/google/common/base/Predicates.java
@@ -169,8 +169,8 @@ public static <T> Predicate<T> equalTo(@Nullable T target) {
    * instances {@code Lists.newArrayList(1)} and {@code Arrays.asList(1)}.
    */
   @GwtIncompatible // Class.isInstance
-  public static Predicate<Object> instanceOf(Class<?> clazz) {
-    return new InstanceOfPredicate(clazz);
+  public static <T> Predicate<T> instanceOf(Class<?> clazz) {
+    return new InstanceOfPredicate<T>(clazz);
   }
 
   /**
@@ -472,7 +472,7 @@ public String toString() {
 
   /** @see Predicates#instanceOf(Class) */
   @GwtIncompatible // Class.isInstance
-  private static class InstanceOfPredicate implements Predicate<Object>, Serializable {
+  private static class InstanceOfPredicate<T> implements Predicate<T>, Serializable {
     private final Class<?> clazz;
 
     private InstanceOfPredicate(Class<?> clazz) {
@@ -480,7 +480,7 @@ private InstanceOfPredicate(Class<?> clazz) {
     }
 
     @Override
-    public boolean apply(@Nullable Object o) {
+    public boolean apply(@Nullable T o) {
       return clazz.isInstance(o);
     }
 
@@ -492,7 +492,7 @@ public int hashCode() {
     @Override
     public boolean equals(@Nullable Object obj) {
       if (obj instanceof InstanceOfPredicate) {
-        InstanceOfPredicate that = (InstanceOfPredicate) obj;
+        InstanceOfPredicate<?> that = (InstanceOfPredicate<?>) obj;
         return clazz == that.clazz;
       }
       return false;