/*
* Copyright 2000-2016 JetBrains s.r.o.
*
* 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 org.jetbrains.annotations;
import java.lang.annotation.*;
/**
* Specifies some aspects of the method behavior depending on the arguments. Can be used by tools for advanced data flow analysis.
* Note that this annotation just describes how the code works and doesn't add any functionality by means of code generation.<p>
*
* Method contract has the following syntax:<br>
* contract ::= (clause ';')* clause<br>
* clause ::= args '->' effect<br>
* args ::= ((arg ',')* arg )?<br>
* arg ::= value-constraint<br>
* value-constraint ::= '_' | 'null' | '!null' | 'false' | 'true'<br>
* effect ::= value-constraint | 'fail' <p>
*
* The constraints denote the following:<br>
* <ul>
* <li> _ - any value
* <li> null - null value
* <li> !null - a value statically proved to be not-null
* <li> true - true boolean value
* <li> false - false boolean value
* <li> fail - the method throws an exception, if the arguments satisfy argument constraints
* </ul>
* Examples:<p>
* {@code @Contract("_, null -> null")} - method returns null if its second argument is null<br>
* {@code @Contract("_, null -> null; _, !null -> !null")} - method returns null if its second argument is null and not-null otherwise<br>
* {@code @Contract("true -> fail")} - a typical assertFalse method which throws an exception if {@code true} is passed to it<br>
*
*/
@Documented
@Retention(RetentionPolicy.CLASS)
@Target({ElementType.METHOD, ElementType.CONSTRUCTOR})
public @interface Contract {
/**
* Contains the contract clauses describing causal relations between call arguments and the returned value
*/
String value() default "";
/**
* Specifies that the annotated method has no visible side effects, in the following sense.
* If its return value is not used, removing its invocation won't
* affect program state and change the semantics. Exception throwing is not considered to be a side effect.
*
* "Invisible" side effects (such as logging) that don't affect the "important" program semantics are allowed.<br><br>
*
* This annotation may be used for more precise data flow analysis, and
* to check that the method's return value is actually used in the call place.
*/
boolean pure() default false;
}