Inherit, Attribute & AttrReference

@Inherit

1. This annotation causes all parameters from value attribute to be inherited. Remember that value must be an annotation.
2. Kendal handlers handling value will receive also annotations that inherit parameters from value using @Inherit.
Note that this relation is transitive.

@Attribute

This annotation will add named parameter to all usages of annotated annotation. Use @Attribute.List to add multiple parameters. Parameters will be added to usages of annotation before handlers are called.
Use @AttrReference as placeholder for values of any other attributes.

@AttrReference

Java does not allow using parameters of annotation to define other parameters of the same annotation. But sometimes we want to, so here we introduce annotation that will be replaced with value of another parameter.
It can be used only inside value expression for @Attribute. Some expressions using @AttrReference will cause the compiler to break compilation before annotation processing - in such case @AttrReference will never work. This feature is currently considered a proof of concept showing that it is possible to access other attributes of annotation to define value of attribute.

Example with Clone

Vanilla Java

      public class SomeClass {

          class CsvTransformer {
              String transform(List<Object> inputCollection) {
                  return "imagine here is the original collection serialized to csv";
              }
          }

          @RequestMapping(value = "/method1", method = "POST")
          public List<Object> method1(RequestBody body) {
              List<Object> result = new ArrayList();
                // some logic
                return result;
          }

          @RequestMapping(value = "/method2", method = "POST")
          public List<Object> method2(RequestBody body) {
              List<Object> result = new ArrayList();
                // some logic
                return result;
          }

          @AnotherAnnotation
          @RequestMapping(value = "/method1/csv", method = "POST")
          public String method1Csv(RequestBody body) {
              List<Object> result = new ArrayList();
                // some logic
                return new CsvTransformer().transform(result);
          }

          @AnotherAnnotation
          @RequestMapping(value = "/method2/csv", method = "POST")
          public String method2Csv(RequestBody body) {
              List<Object> result = new ArrayList();
                // some logic
                return new CsvTransformer().transform(result);
          }

          @interface AnotherAnnotation {}
      }
  

Kendal without @Inherit

Impossible!

Kendal with @Inherit

      public class SomeClass {

          @Inherit(@Clone(transformer = CsvTransformer.class))
          @Attribute(name = "onMethod", value = {@RequestMapping(value = @AttrReference("endpoint"), method = "POST"),
                                                  @AnotherAnnotation})
          @interface CsvEndpoint {
              String endpoint();
          }

          class CsvTransformer implements Clone.Transformer<List<Object>, String> {
              @Override
              public String transform(List<Object> inputCollection) {
                  return "imagine here is the original collection serialized to csv";
              }
          }

          @CsvEndpoint(endpoint = "method1/csv", methodName = "method1Csv")
          @RequestMapping(value = "/method1", method = "POST")
          public List<Object> method1(RequestBody body) {
              List<Object> result = new ArrayList();
                // some logic
                return result;
          }

          @CsvEndpoint(endpoint = "method2/csv", methodName = "method2Csv")
          @RequestMapping(value = "/method2", method = "POST")
          public List<Object> method2(RequestBody body) {
              List<Object> result = new ArrayList();
                // some logic
                return result;
          }

          @interface AnotherAnnotation {}
      }
  

Example with TypeScript Fields

Vanilla Java

      class SomeClass {

          int primitiveField;

          SomeClass(int primitiveField) {
              this.primitiveField = primitiveField;
          }

          private int aMethod() {
              return this.primitiveField + 15;
          }
      }
  

Kendal without @Inherit

      class SomeClass {

          SomeClass(@Private(makeFinal = false) int primitiveField) { }

          private int aMethod() {
              return this.primitiveField + 15;
          }
      }
  

Kendal with @Inherit

      class SomeClass {

          SomeClass(@PrivateNotFinal int primitiveField) { }

          private int aMethod() {
              return this.primitiveField + 15;
          }

          @Inherit(@Private(makeFinal = false))
          @Target(ElementType.PARAMETER)
          @interface PrivateNotFinal { }
      }