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

Author: cpovirk

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;

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);
   }
 
   /**
@@ -472,15 +472,15 @@ 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) {
       this.clazz = checkNotNull(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;

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;

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);
   }
 
   /**
@@ -472,15 +472,15 @@ 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) {
       this.clazz = checkNotNull(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;