丰富函数式编程接口。

src/main/java/xyz/zhouxy/plusone/commons/function/DoubleToOptionalFunction.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.Optional;
+import java.util.function.DoubleFunction;
+
+@FunctionalInterface
+public interface DoubleToOptionalFunction<R> extends DoubleFunction<Optional<R>> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/IntToOptionalFunction.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.Optional;
+import java.util.function.IntFunction;
+
+@FunctionalInterface
+public interface IntToOptionalFunction<R> extends IntFunction<Optional<R>> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/LongToOptionalFunction.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.Optional;
+import java.util.function.LongFunction;
+
+@FunctionalInterface
+public interface LongToOptionalFunction<R> extends LongFunction<Optional<R>> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/OptionalDoubleSupplier.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.OptionalDouble;
+import java.util.function.Supplier;
+
+@FunctionalInterface
+public interface OptionalDoubleSupplier extends Supplier<OptionalDouble> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/OptionalIntSupplier.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.OptionalInt;
+import java.util.function.Supplier;
+
+@FunctionalInterface
+public interface OptionalIntSupplier extends Supplier<OptionalInt> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/OptionalLongSupplier.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.OptionalLong;
+import java.util.function.Supplier;
+
+@FunctionalInterface
+public interface OptionalLongSupplier extends Supplier<OptionalLong> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/OptionalSupplier.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.Optional;
+import java.util.function.Supplier;
+
+@FunctionalInterface
+public interface OptionalSupplier<T> extends Supplier<Optional<T>> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/ToOptionalBiFunction.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.Optional;
+import java.util.function.BiFunction;
+
+@FunctionalInterface
+public interface ToOptionalBiFunction<T, U, R> extends BiFunction<T, U, Optional<R>> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/ToOptionalDoubleFunction.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.OptionalDouble;
+import java.util.function.Function;
+
+@FunctionalInterface
+public interface ToOptionalDoubleFunction<T> extends Function<T, OptionalDouble> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/ToOptionalFunction.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.Optional;
+import java.util.function.Function;
+
+@FunctionalInterface
+public interface ToOptionalFunction<T, R> extends Function<T, Optional<R>> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/ToOptionalIntFunction.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.OptionalInt;
+import java.util.function.Function;
+
+@FunctionalInterface
+public interface ToOptionalIntFunction<T> extends Function<T, OptionalInt> {
+}

src/main/java/xyz/zhouxy/plusone/commons/function/ToOptionalLongFunction.java

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+package xyz.zhouxy.plusone.commons.function;
+
+import java.util.OptionalLong;
+import java.util.function.Function;
+
+@FunctionalInterface
+public interface ToOptionalLongFunction<T> extends Function<T, OptionalLong> {
+}