CheckedFunction.java

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package com.google.mu.function;

import static java.util.Objects.requireNonNull;

/** A function that can throw checked exceptions. */
@FunctionalInterface
public interface CheckedFunction<F, T, E extends Throwable> {
  T apply(F from) throws E;

  /**
   * Returns a new {@code CheckedFunction} that maps the return value using {@code mapper}.
   * For example: {@code (x -> x).andThen(Object::toString).apply(1) => "1"}.
   */
  default <R> CheckedFunction<F, R, E> andThen(
      CheckedFunction<? super T, ? extends R, ? extends E> mapper) {
    requireNonNull(mapper);
    return f -> mapper.apply(apply(f));
  }
}