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optionals/.project

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+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>optionals</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>

optionals/.settings/org.eclipse.core.resources.prefs

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+eclipse.preferences.version=1
+encoding/<project>=UTF-8

optionals/.settings/org.eclipse.jdt.core.prefs

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+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=21
+org.eclipse.jdt.core.compiler.codegen.unusedLocal=preserve
+org.eclipse.jdt.core.compiler.compliance=21
+org.eclipse.jdt.core.compiler.debug.lineNumber=generate
+org.eclipse.jdt.core.compiler.debug.localVariable=generate
+org.eclipse.jdt.core.compiler.debug.sourceFile=generate
+org.eclipse.jdt.core.compiler.problem.enablePreviewFeatures=disabled
+org.eclipse.jdt.core.compiler.problem.reportPreviewFeatures=warning
+org.eclipse.jdt.core.compiler.release=enabled
+org.eclipse.jdt.core.compiler.source=21

optionals/src/optionals/Main.java

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+package optionals;
+
+import java.util.List;
+import java.util.Optional;
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+class OptionalUtils {
+    // Return the list of `f()` applied to every element in `xs`, but do not
+    // include the empty results.
+    static <X, Y> List<Y>
+    convertPassing(List<X> xs, Function<X, Optional<Y>> f) {
+        return null;
+    }
+
+    // Return the list of `f()` applied to every element in `xs`, but do not
+    // include the resuslts that don't pass `pred()`.
+    static <X, Y> List<Y>
+    convertPassing(List<X> xs, Function<X, Y> f, Predicate<Y> pred) {
+        return null;
+    }
+
+    // Drop all empty values.
+    static <X> List<X> dropEmpty(List<Optional<X>> xs) {
+        return xs.stream().filter(Optional::isEmpty);
+    }
+
+    // Return a new function that applies `f()` to non-null values and returns
+    // empty optionals on null values.
+    static <X, Y> Function<X, Optional<Y>> nullFriendly(Function<X, Y> f) {
+        return null;
+    }
+
+    // Apply and to the boolean values if both are present, otherwise return
+    // empty optional.
+    static Optional<Boolean>
+    optionalAnd(Optional<Boolean> b1, Optional<Boolean> b2) {
+        return null;
+    }
+}
+
+class Examples {}