add com.google.common

Author: shuwenwei

iotdb-core/node-commons/src/main/java/com/google/common/base/Ascii.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2021 The Guava Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package com.google.common.base;
+
+import javax.annotation.CheckForNull;
+
+/** A utility method to perform unchecked casts to suppress errors produced by nullness analyses. */
+final class NullnessCasts {
+  /**
+   * Accepts a {@code @Nullable T} and returns a plain {@code T}, without performing any check that
+   * that conversion is safe.
+   *
+   * <p>This method is intended to help with usages of type parameters that have {@linkplain
+   * ParametricNullness parametric nullness}. If a type parameter instead ranges over only non-null
+   * types (or if the type is a non-variable type, like {@code String}), then code should almost
+   * never use this method, preferring instead to call {@code requireNonNull} so as to benefit from
+   * its runtime check.
+   *
+   * <p>An example use case for this method is in implementing an {@code Iterator<T>} whose {@code
+   * next} field is lazily initialized. The type of that field would be {@code @Nullable T}, and the
+   * code would be responsible for populating a "real" {@code T} (which might still be the value
+   * {@code null}!) before returning it to callers. Depending on how the code is structured, a
+   * nullness analysis might not understand that the field has been populated. To avoid that problem
+   * without having to add {@code @SuppressWarnings}, the code can call this method.
+   *
+   * <p>Why <i>not</i> just add {@code SuppressWarnings}? The problem is that this method is
+   * typically useful for {@code return} statements. That leaves the code with two options: Either
+   * add the suppression to the whole method (which turns off checking for a large section of code),
+   * or extract a variable, and put the suppression on that. However, a local variable typically
+   * doesn't work: Because nullness analyses typically infer the nullness of local variables,
+   * there's no way to assign a {@code @Nullable T} to a field {@code T foo;} and instruct the
+   * analysis that that means "plain {@code T}" rather than the inferred type {@code @Nullable T}.
+   * (Even if supported added {@code @NonNull}, that would not help, since the problem case
+   * addressed by this method is the case in which {@code T} has parametric nullness -- and thus its
+   * value may be legitimately {@code null}.)
+   */
+  @SuppressWarnings("nullness")
+  static <T extends Object> T uncheckedCastNullableTToT(@CheckForNull T t) {
+    return t;
+  }
+
+  private NullnessCasts() {}
+}