Class annotation to make constructors from a super class available in a sub class. Should be used with care with other annotations which create constructors - see "Known Limitations" for more details.

@InheritConstructors saves you typing some boilerplate code.

Example usage:

class Person {
    String first, last
    Person(String first, String last) {
        this.first = first
        this.last = last.toUpperCase()
    }
}

@groovy.transform.InheritConstructors
class PersonAge extends Person {
    int age
}

def js = new PersonAge('John', 'Smith')
js.age = 25

assert "$js.last, $js.first is $js.age years old" == 'SMITH, John is 25 years old'

for this case, the PersonAge class will be equivalent to the following code:

class PersonAge extends Person {
    PersonAge(String first, String last) {
        super(first, last)
    }
    int age
}

You may add additional constructors in addition to inherited ones. If the argument types of a supplied constructor exactly match those of a parent constructor, then that constructor won't be inherited.

Style note: Don't go overboard using this annotation. Typical Groovy style is to use named-arg constructors when possible. This is easy to do for Groovy objects or any objects following JavaBean conventions. In other cases, inheriting the constructors may be useful. However, sub-classes often introduce new properties and these are often best set in a constructor; especially if that matches the style adopted in parent classes. So, even for the example above, it may have been better style to define an explicit constructor for PersonAge that also set the age property. Sometimes, consistent style is much more important than saving a few keystrokes.

As another example, this:

@InheritConstructors class CustomException extends RuntimeException { }

is equivalent to this:

class CustomException extends RuntimeException {
    CustomException() {
        super()
    }
    CustomException(String message) {
        super(message)
    }
    CustomException(String message, Throwable cause) {
        super(message, cause)
    }
    CustomException(Throwable cause) {
        super(cause)
    }
}

Known Limitations:

• This AST transform creates (potentially) numerous constructors. You should take care to avoid constructors with duplicate signatures if you are defining your own constructors or combining with other AST transforms which create constructors (e.g. @TupleConstructor); the order in which the particular transforms are processed becomes important in that case.
• If you create Groovy constructors with optional arguments this leads to multiple constructors created in the byte code. The expansion to multiple constructors occurs in a later phase to this AST transformation. This means that you can't override (i.e. not inherit) the constructors with signatures that Groovy adds later. If you get it wrong you will get a compile-time error about the duplication.

More examples:

//--------------------------------------------------------------------------
import groovy.transform.InheritConstructors

@InheritConstructors
class MyException extends Exception {
}

def e = new MyException()
def e1 = new MyException('message')   // Other constructors are available.
assert 'message' == e1.message

//--------------------------------------------------------------------------
import groovy.transform.InheritConstructors

class Person {
    String name

    Person(String name) {
        this.name = name
    }
}

@InheritConstructors
class Child extends Person {}

def child = new Child('Liam')
assert 'Liam' == child.name