io.opencensus.common.Functions Maven / Gradle / Ivy
/*
* 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 RETURN_NULL =
new Function() {
@Override
@javax.annotation.Nullable
public Void apply(Object ignored) {
return null;
}
};
private static final Function THROW_ILLEGAL_ARGUMENT_EXCEPTION =
new Function() {
@Override
public Void apply(Object ignored) {
throw new IllegalArgumentException();
}
};
private static final Function THROW_ASSERTION_ERROR =
new Function() {
@Override
public Void apply(Object ignored) {
throw new AssertionError();
}
};
private static final Function RETURN_TO_STRING =
new Function() {
@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 Function returnNull() {
// It is safe to cast a producer of Void to anything, because Void is always null.
@SuppressWarnings("unchecked")
Function function = (Function) 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 Function returnConstant(final T constant) {
return new Function() {
@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 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 Function throwIllegalArgumentException() {
// It is safe to cast this function to have any return type, since it never returns a result.
@SuppressWarnings("unchecked")
Function function = (Function) 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 Function throwAssertionError() {
// It is safe to cast this function to have any return type, since it never returns a result.
@SuppressWarnings("unchecked")
Function function = (Function) THROW_ASSERTION_ERROR;
return function;
}
}