Dependent.java

package org.checkerframework.framework.qual;

import java.lang.annotation.Annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Refines the qualified type of the annotated field or variable based on the qualified type of the
 * receiver. The annotation declares a relationship between multiple type qualifier hierarchies.
 *
 * <p><b>Example:</b> Consider a field, {@code lock}, that is only initialized if the enclosing
 * object (the receiver), is marked as {@code ThreadSafe}. Such a field can be declared as:
 *
 * <pre>{@code
 * private @Nullable @Dependent(result=NonNull.class, when=ThreadSafe.class)
 *   Lock lock;
 * }</pre>
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER})
public @interface Dependent {

    /** The class of the refined qualifier to be applied. */
    Class<? extends Annotation> result();

    /**
     * The qualifier class of the receiver that causes the {@code result} qualifier to be applied.
     */
    Class<? extends Annotation> when();
}