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package com.oracle.truffle.api.dsl;
import com.oracle.truffle.api.nodes.Node;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
*
* A method annotated with {@link Fallback} is treated as a {@link Specialization} that implicitly
* links all the guards of all other declared {@link Specialization} annotated methods of the
* operation in a negated form. As a consequence it cannot declare any other guards. The expected
* signature of the method must match to the signature of a {@link Specialization} with the
* additional limitation that only generically executable argument types are allowed. A generically
* executable argument is an argument that can be executed from the child {@link Node} using an
* execute method without {@link UnsupportedOperationException}. In many cases the generically
* executable type is {@link Object}. An operation is limited to just one {@link Fallback}
* specialization which is always ordered at the end of the specialization chain.
*
*
*
* A simple example showing the use of the {@link Fallback} annotation in a DSL operation:
*
*
*
* @Specialization int doInt(int a) {..}
* @Specialization int doDouble(double a) {..}
* @Fallback int orElse(Object a) {..}
*
*
*
* The previous example could be redeclared just using {@link Specialization} annotated methods as
* follows:
*
*
*
* @Specialization int doInt(int a) {..}
* @Specialization int doDouble(double a) {..}
* @Specialization(guard={"!isInt(a)", "!isDouble(a)"})
* int orElse(Object a) {..}
*
*
*
* Performance note: For operations with a lot of {@link Specialization} annotated methods
* the use of {@link Fallback} might generate a guard that is very big. Try to avoid the use of
* {@link Fallback} for specializations that are significantly important for peak performance.
*
*
* @see Specialization
* @see NodeChild
* @since 0.8 or earlier
*/
@Retention(RetentionPolicy.CLASS)
@Target({ElementType.METHOD})
public @interface Fallback {
}