https://github.com/ReactiveX/RxJava: Reactive Extensions for Java
  • David Karnok 
Copyright (c) 2016-present, RxJava Contributors.
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.

/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * 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.reactivex.internal.fuseable;

import java.util.concurrent.Callable;


A marker interface indicating that a scalar, constant value
is held by the implementing reactive type which can be
safely extracted during assembly time can be used for
optimization.

 Implementors of call() should not throw any exception. 
 Design note: the interface extends Callable because if a scalar is safe to extract during assembly time, it is also safe to extract at subscription time or later. This allows optimizations to deal with such single-element sources uniformly. 


Type parameters:
  • <T> – the scalar value type held by the implementing reactive type
/**
 * A marker interface indicating that a scalar, constant value
 * is held by the implementing reactive type which can be
 * safely extracted during assembly time can be used for
 * optimization.
 * <p>
 * Implementors of {@link #call()} should not throw any exception.
 * <p>
 * Design note: the interface extends {@link Callable} because if a scalar
 * is safe to extract during assembly time, it is also safe to extract at
 * subscription time or later. This allows optimizations to deal with such
 * single-element sources uniformly.
 * <p>
 * @param <T> the scalar value type held by the implementing reactive type
 */
public interface ScalarCallable<T> extends Callable<T> {

    // overridden to remove the throws Exception
    @Override
    T call();
}