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/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file, and Oracle licenses the original version of this file under the BSD
* license:
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/*
Copyright 2009-2013 Attila Szegedi
Licensed under both the Apache License, Version 2.0 (the "Apache License")
and the BSD License (the "BSD License"), with licensee being free to
choose either of the two at their discretion.
You may not use this file except in compliance with either the Apache
License or the BSD License.
If you choose to use this file in compliance with the Apache License, the
following notice applies to you:
You may obtain a copy of the Apache 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.
If you choose to use this file in compliance with the BSD License, the
following notice applies to you:
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
* Neither the name of the copyright holder nor the names of
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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*/
package jdk.dynalink.linker;
import java.lang.invoke.MethodHandles;
import java.util.function.Supplier;
import jdk.dynalink.SecureLookupSupplier;
import jdk.dynalink.beans.BeansLinker;
import jdk.dynalink.linker.support.TypeUtilities;
/**
* Optional interface that can be implemented by {@link GuardingDynamicLinker}
* implementations to provide language-specific type conversion capabilities.
* Note that if you implement this interface, you will very likely want to
* implement {@link ConversionComparator} interface too, as your additional
* language-specific conversions, in absence of a strategy for prioritizing
* these conversions, will cause more ambiguity for {@link BeansLinker} in
* selecting the correct overload when trying to link to an overloaded Java
* method.
*/
public interface GuardingTypeConverterFactory {
/**
* Returns a guarded type conversion that receives a value of the specified
* source type and returns a value converted to the specified target type.
* Value types can be either primitives or reference types, including
* interfaces, so you can even provide converters for converting your
* language's objects to Java interfaces and classes by generating adapters
* for them.
* <p>
* The type of the invocation is <tt>(sourceType)→targetType</tt>, while the
* type of the guard is <tt>(sourceType)→boolean</tt>. You are allowed to
* return unconditional invocations (with no guard) if the source type is
* specific to your runtime and your runtime only.
* <p>Note that this method will never be invoked for
* {@link TypeUtilities#isMethodInvocationConvertible(Class, Class) method
* invocation conversions} as those can be automatically applied by
* {@link java.lang.invoke.MethodHandle#asType(MethodType)}.
* An implementation can assume it is never requested to produce a
* converter for those conversions. If a language runtime needs to customize
* method invocation conversions, it should
* {@link jdk.dynalink.DynamicLinkerFactory#setAutoConversionStrategy(MethodTypeConversionStrategy)
* set an autoconversion strategy in the dynamic linker factory} instead.
* <p>Dynalink is at liberty to either cache some of the returned converters
* or to repeatedly request the converter factory to create the same
* conversion.
*
* @param sourceType source type
* @param targetType the target type.
* @param lookupSupplier a supplier for retrieving the lookup of the class
* on whose behalf a type converter is requested. When a converter is
* requested as part of linking an {@code invokedynamic} instruction the
* supplier will return the lookup passed to the bootstrap method, otherwise
* if the method is invoked from within a
* {@link LinkerServices#getWithLookup(Supplier, jdk.dynalink.SecureLookupSupplier)}
* it will delegate to the secure lookup supplier. In any other case,
* it will return the public lookup. A typical case where the lookup might
* be needed is when the converter creates a Java adapter class on the fly
* (e.g. to convert some object from the dynamic language into a Java
* interface for interoperability). Invoking the {@link Supplier#get()}
* method on the passed supplier will be subject to the same security checks
* as {@link SecureLookupSupplier#getLookup()}. An implementation should avoid
* retrieving the lookup if it is not needed so as to avoid the expense of
* {@code AccessController.doPrivileged} call.
* @return a guarded invocation that can take an object (if it passes guard)
* and return another object that is its representation coerced into the
* target type. In case the factory is certain it is unable to handle a
* conversion, it can return null. In case the factory is certain that it
* can always handle the conversion, it can return an unconditional
* invocation (one whose guard is null).
* @throws Exception if there was an error during creation of the converter
* @see LinkerServices#getWithLookup(Supplier, SecureLookupSupplier)
*/
public GuardedInvocation convertToType(Class<?> sourceType, Class<?> targetType, Supplier<MethodHandles.Lookup> lookupSupplier) throws Exception;
}