kafka.utils.NotNothing.scala Maven / Gradle / Ivy
/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 kafka.utils
import scala.annotation.implicitNotFound
/**
* This is a trick to prevent the compiler from inferring the `Nothing` type in cases where it would be a bug to do
* so. An example is the following method:
*
* ```
* def body[T <: AbstractRequest](implicit classTag: ClassTag[T], nn: NotNothing[T]): T
* ```
*
* If we remove the `nn` parameter and we invoke it without any type parameters (e.g. `request.body`), `Nothing` would
* be inferred, which is not desirable. As defined above, we get a helpful compiler error asking the user to provide
* the type parameter explicitly.
*/
@implicitNotFound("Unable to infer type parameter, please provide it explicitly.")
trait NotNothing[T]
object NotNothing {
private val evidence: NotNothing[Any] = new Object with NotNothing[Any]
implicit def notNothingEvidence[T](implicit n: T =:= T): NotNothing[T] = evidence.asInstanceOf[NotNothing[T]]
}