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/*
* Copyright 2017, OpenCensus 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 io.opencensus.common;
/*>>>
import org.checkerframework.checker.nullness.qual.Nullable;
*/
/**
* Commonly used {@link Function} instances.
*
* @since 0.5
*/
public final class Functions {
private Functions() {}
private static final Function<Object, /*@Nullable*/ Void> RETURN_NULL =
new Function<Object, /*@Nullable*/ Void>() {
@Override
@javax.annotation.Nullable
public Void apply(Object ignored) {
return null;
}
};
private static final Function<Object, Void> THROW_ILLEGAL_ARGUMENT_EXCEPTION =
new Function<Object, Void>() {
@Override
public Void apply(Object ignored) {
throw new IllegalArgumentException();
}
};
private static final Function<Object, Void> THROW_ASSERTION_ERROR =
new Function<Object, Void>() {
@Override
public Void apply(Object ignored) {
throw new AssertionError();
}
};
private static final Function<Object, /*@Nullable*/ String> RETURN_TO_STRING =
new Function<Object, /*@Nullable*/ String>() {
@Override
public /*@Nullable*/ String apply(Object input) {
return input == null ? null : input.toString();
}
};
/**
* A {@code Function} that always ignores its argument and returns {@code null}.
*
* @return a {@code Function} that always ignores its argument and returns {@code null}.
* @since 0.5
*/
public static <T> Function<Object, /*@Nullable*/ T> returnNull() {
// It is safe to cast a producer of Void to anything, because Void is always null.
@SuppressWarnings("unchecked")
Function<Object, /*@Nullable*/ T> function = (Function<Object, /*@Nullable*/ T>) RETURN_NULL;
return function;
}
/**
* A {@code Function} that always ignores its argument and returns a constant value.
*
* @return a {@code Function} that always ignores its argument and returns a constant value.
* @since 0.5
*/
public static <T> Function<Object, T> returnConstant(final T constant) {
return new Function<Object, T>() {
@Override
public T apply(Object ignored) {
return constant;
}
};
}
/**
* A {@code Function} that always returns the {@link #toString()} value of the input.
*
* @return a {@code Function} that always returns the {@link #toString()} value of the input.
* @since 0.17
*/
public static Function<Object, /*@Nullable*/ String> returnToString() {
return RETURN_TO_STRING;
}
/**
* A {@code Function} that always ignores its argument and throws an {@link
* IllegalArgumentException}.
*
* @return a {@code Function} that always ignores its argument and throws an {@link
* IllegalArgumentException}.
* @since 0.5
*/
public static <T> Function<Object, T> throwIllegalArgumentException() {
// It is safe to cast this function to have any return type, since it never returns a result.
@SuppressWarnings("unchecked")
Function<Object, T> function = (Function<Object, T>) THROW_ILLEGAL_ARGUMENT_EXCEPTION;
return function;
}
/**
* A {@code Function} that always ignores its argument and throws an {@link AssertionError}.
*
* @return a {@code Function} that always ignores its argument and throws an {@code
* AssertionError}.
* @since 0.6
*/
public static <T> Function<Object, T> throwAssertionError() {
// It is safe to cast this function to have any return type, since it never returns a result.
@SuppressWarnings("unchecked")
Function<Object, T> function = (Function<Object, T>) THROW_ASSERTION_ERROR;
return function;
}
}
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