This strategy is used with the
Builder AST transform to create a builder helper class
for the fluent and type-safe creation of instances of a specified class.
It is modelled roughly on the design outlined here:
http://michid.wordpress.com/2008/08/13/type-safe-builder-pattern-in-java/
You define classes which use the type-safe initializer pattern as follows:
import groovy.transform.builder.*
import groovy.transform.*
@ToString
@Builder(builderStrategy=InitializerStrategy) class Person {
String firstName
String lastName
int age
}
While it isn't required to do so, the benefit of this builder strategy comes in conjunction with static type-checking or static compilation. Typical usage is as follows:
@CompileStatic
def main() {
println new Person(Person.createInitializer().firstName("John").lastName("Smith").age(21))
}
which prints:
Person(John, Smith, 21)
If you don't initialise some of the properties, your code won't compile, e.g. if the method body above was changed to this:
println new Person(Person.createInitializer().firstName("John").lastName("Smith"))
then the following compile-time error would result:
[Static type checking] - Cannot find matching method Person#(Person$PersonInitializer ). Please check if the declared type is right and if the method exists.
The message is a little cryptic, but it is basically the static compiler telling us that the third parameter,
age in our case, is unset.