001package arez.annotations;
002
003import arez.ObservableValue;
004import java.lang.annotation.Documented;
005import java.lang.annotation.ElementType;
006import java.lang.annotation.Target;
007import javax.annotation.Nonnull;
008
009/**
010 * Marks a template method that returns the {@link ObservableValue} instance for
011 * the {@link Observable} annotated property. Each property marked with the {@link Observable} annotation is backed
012 * by an {@link ObservableValue} instance and some frameworks make use of this value to implement
013 * advanced functionality.
014 *
015 * <p>The method that is annotated with this annotation must also comply with the following constraints:</p>
016 * <ul>
017 * <li>Must not be annotated with any other arez annotation</li>
018 * <li>Must be abstract</li>
019 * <li>Must not throw any exceptions</li>
020 * <li>Must be accessible to the class annotated by the {@link ArezComponent} annotation.</li>
021 * <li>
022 *   Must return an instance of {@link ObservableValue} and the type parameter must be the
023 *   wildcard {@code ?} or the type of the corresponding {@link Observable} method. The value
024 *   may also be "raw" (i.e. without a type parameter).
025 * </li>
026 * <li>
027 *   Should not be public as not expected to be invoked outside the component. A warning will be generated but can
028 *   be suppressed by the {@link SuppressWarnings} or {@link SuppressArezWarnings} annotations with a key
029 *   "Arez:PublicRefMethod". This warning is also suppressed by the annotation processor if it is implementing
030 *   an interface method.
031 * </li>
032 * <li>
033 *   Should not be protected if in the class annotated with the {@link ArezComponent} annotation as the method is not
034 *   expected to be invoked outside the component. A warning will be generated but can be suppressed by the
035 *   {@link SuppressWarnings} or {@link SuppressArezWarnings} annotations with a key "Arez:ProtectedMethod".
036 * </li>
037 * </ul>
038 */
039@Documented
040@Target( ElementType.METHOD )
041public @interface ObservableValueRef
042{
043  /**
044   * Return the name of the associated ObservableValue property that this ref relates to.
045   * This value will be derived if the method name matches the pattern "get[Name]ObservableValue",
046   * otherwise it must be specified.
047   *
048   * @return the name of the associated ObservableValue.
049   */
050  @Nonnull
051  String name() default "<default>";
052}