Package groovy.contracts

# Annotation Type Ensures

@Retention(RUNTIME) @Target({CONSTRUCTOR,METHOD}) @Incubating @Postcondition @AnnotationProcessorImplementation(EnsuresAnnotationProcessor.class) public @interface Ensures

Represents a method postcondition.

A postcondition is a condition that is guaranteed to be fulfilled by suppliers.

A method's postcondition is executed after a method call has finished. A successor's postcondition strengthens the postcondition of its parent class, e.g. if A.someMethod declares a postcondition and B.someMethod overrides the method the postconditions are combined with a boolean AND.

Compared to pre-conditions, postcondition annotation closures are optionally called with two additional closure arguments: `result` and `old`.

`result` is available if the corresponding method has a non-void return-type and holds the result of the method call. Be aware that modifying the internal state of a reference type can lead to side-effects. Groovy-contracts does not keep track of any sort of modifications, neither any conversion to immutability.

`old` is available in every postcondition. It is a `Map` which holds the values of value types and `Cloneable` types before the method has been executed.

Examples:

Accessing the `result` closure parameter:

       @Ensures({ result -> result != argument1 })
       def T someOperation(def argument1, def argument2)  {
         ...
       }

Accessing the `old` closure parameter:

       @Ensures({ old -> old.counter + 1 == counter })
       def T someOperation(def argument1, def argument2)  {
         ...
       }

- ## Required Element Summary

  Required Elements
  Modifier and Type
  Required Element
  Description
  `Class`
  `value`

- ## Element Details

  - ### value

    Class value