Package org.apache.groovy.contracts.ast

Class LoopVariantASTTransformation

java.lang.Object
org.apache.groovy.contracts.ast.LoopVariantASTTransformation
All Implemented Interfaces:
ASTTransformation
public class LoopVariantASTTransformation extends Object implements ASTTransformation
Handles Decreases annotations placed on loop statements (for, while, do-while). The closure must return a value that strictly decreases on every iteration and remains non-negative.

The transformation injects code to:

  1. Save the expression value at the start of each iteration.
  2. Re-evaluate it at the end of the iteration.
  3. Assert the value has strictly decreased.
  4. Assert the value is non-negative.

Example: 

 int n = 10
 @Decreases({ n })
 while (n > 0) {
     n--
 }
Since:
6.0.0
See Also:

  • Constructor Details

    • LoopVariantASTTransformation

      public LoopVariantASTTransformation()

  • Method Details

    • visit

      public void visit(ASTNode[] nodes, SourceUnit source)
      Description copied from interface: ASTTransformation
      The method is invoked when an AST Transformation is active. For local transformations, it is invoked once each time the local annotation is encountered. For global transformations, it is invoked once for every source unit, which is typically a source file.
      Specified by:
      visit in interface ASTTransformation
      Parameters:
      nodes - The ASTnodes when the call was triggered. Element 0 is the AnnotationNode that triggered this annotation to be activated. Element 1 is the AnnotatedNode decorated, such as a MethodNode or ClassNode. For global transformations it is usually safe to ignore this parameter.
      source - The source unit being compiled. The source unit may contain several classes. For global transformations, information about the AST can be retrieved from this object.

    • checkDecreased

      public static void checkDecreased(Object prev, Object curr)
      Runtime check called from generated code. Throws LoopVariantViolation if the variant did not strictly decrease or became negative.

      If both values are Lists, they are compared lexicographically: the first position where values differ must show a strict decrease; all earlier positions must be equal. If all positions are equal, the variant has not decreased and a violation is thrown.