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Annotations for use in Swift interfaces and types
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/*
 * Copyright (C) 2012 Facebook, Inc.
 *
 * Licensed 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 com.facebook.swift.codec;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Marks a field, method or parameter as a Thrift field.
 */
@Documented
@Retention(RUNTIME)
@Target({METHOD, FIELD, PARAMETER})
public @interface ThriftField
{
    String RECURSIVE_REFERENCE_ANNOTATION_NAME = "swift.recursive_reference";

    short value() default Short.MIN_VALUE;

    /** Indicates this ThriftField has a negative ID, which is deprecated. */
    boolean isLegacyId() default false;

    String name() default "";

    Requiredness requiredness() default Requiredness.UNSPECIFIED;

    Recursiveness isRecursive() default Recursiveness.UNSPECIFIED;

    ThriftIdlAnnotation[] idlAnnotations() default {};

    enum Recursiveness
    {
        UNSPECIFIED,
        FALSE,
        TRUE,
    }

    /**
     * Indicates the behavior for a field when a value is not received, or when the value
     * of the field is not set when sending.
     */
    enum Requiredness
    {
        /**
         * This is the default (unset) value for {@link ThriftField#requiredness()}. It will not
         * conflict with other explicit settings of {@link #NONE}, {@link #REQUIRED}, or {@link
         * #OPTIONAL}. If all of the {@link com.facebook.swift.codec.ThriftField} annotations for
         * a field are left {@link #UNSPECIFIED}, it will default to {@link #NONE}.
         */
        UNSPECIFIED,
        /**
         * This behavior is equivalent to leaving out 'optional' and 'required' in thrift IDL
         * syntax. However, despite the name, this actually does correspond to defined behavior so
         * if this value is explicitly specified in any annotations, it will conflict with other
         * annotations that specify either {@link #OPTIONAL} or {@link #REQUIRED} for the same
         * field.
         *
         * The serialization behavior is that {@code null} values will not be serialized, but
         * if the field is non-nullable (i.e. it's type is primitive) it will be serialized, even
         * if the field was not explicitly set.
         *
         * The deserialization behavior is similar: When no value is read, the field will be set
         * to {@code null} if the type of the field is nullable, but for primitive types the
         * field will be left untouched (so it will hold the default value for the type).
         */
        NONE,
        /**
         * This behavior indicates that the field will always be serialized (and it is an error if the
         * value is {@code null}), and must always be deserialized (and it is an error if a value
         * is not read).
         */
        REQUIRED,
        /**
         * This behavior indicates that it is always ok if the field is {@code null} when serializing,
         * and that it is always ok to not read a value (and the field will be set to {@code null}
         * when this happens). As such, primitive types should be replaced with boxed types, so that
         * null is always a possibility.
         */
        OPTIONAL
    }
}