Package groovy.contracts

Annotation Interface Invariant

@Documented @Retention(RUNTIME) @Target(TYPE) @Incubating @ClassInvariant @Repeatable(Invariants.class) @AnnotationProcessorImplementation(ClassInvariantAnnotationProcessor.class) public @interface Invariant

Represents a class-invariant or a loop invariant.

When applied to a class, defines assertions holding during the entire object's life-time. Class-invariants are verified at runtime at the following pointcuts:

  • after a constructor call
  • before a method call
  • after a method call

When applied to a for, while, or do-while loop, defines a loop invariant that is asserted at the start of each iteration: 

 int sum = 0
 @Invariant({ 0 <= i && i <= 4 })
 for (int i in 0..4) {
     sum += i
 }

Whenever a class has a parent which itself specifies a class-invariant, that class-invariant expression is combined with the actual class's invariant (by using a logical AND).

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