groovy.lang.TrampolineClosure Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* distributed with this work for additional information
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* 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 groovy.lang;
/**
* A TrampolineClosure wraps a closure that needs to be executed on a functional trampoline.
* Upon calling, a TrampolineClosure will call the original closure waiting for its result.
* If the outcome of the call is another instance of a TrampolineClosure, created perhaps as a result to a call to the TrampolineClosure.trampoline()
* method, the TrampolineClosure will again be invoked. This repetitive invocation of returned TrampolineClosure instances will continue
* until a value other than TrampolineClosure is returned.
* That value will become the final result of the trampoline.
*
* @author Vaclav Pech
*/
final class TrampolineClosure extends Closure {
private static final long serialVersionUID = -4096349147398489925L;
private final Closure original;
TrampolineClosure(final Closure original) {
super(original.getOwner(), original.getDelegate());
this.original = original;
}
/**
* Delegates to the wrapped closure
*/
@Override
public int getMaximumNumberOfParameters() {
return original.maximumNumberOfParameters;
}
/**
* Delegates to the wrapped closure
*/
@Override
public Class[] getParameterTypes() {
return original.parameterTypes;
}
/**
* Starts the trampoline loop and calls the wrapped closure as the first step.
* @return The final result of the trampoline
*/
@Override
public V call() {
return loop(original.call());
}
/**
* Starts the trampoline loop and calls the wrapped closure as the first step.
* @return The final result of the trampoline
*/
@Override
public V call(final Object arguments) {
return loop(original.call(arguments));
}
/**
* Starts the trampoline loop and calls the wrapped closure as the first step.
* @return The final result of the trampoline
*/
@Override
public V call(final Object... args) {
return loop(original.call(args));
}
private V loop(final Object lastResult) {
Object result = lastResult;
for (;;) {
if (result instanceof TrampolineClosure) {
result = ((TrampolineClosure)result).original.call();
} else return (V) result;
}
}
/**
* Builds a trampolined variant of the current closure.
* @param args Parameters to curry to the underlying closure.
* @return An instance of TrampolineClosure wrapping the original closure after currying.
*/
@Override
public Closure trampoline(final Object... args) {
return new TrampolineClosure(original.curry(args));
}
/**
* Returns itself, since it is a good enough trampolined variant of the current closure.
* @return An instance of TrampolineClosure wrapping the original closure.
*/
@Override
public Closure trampoline() {
return this;
}
}