DelegatesTo + generic

configurable.groovy

import groovy.transform.CompileStatic

public <T> T configure(@DelegatesTo.Target Class<T> clazz, @DelegatesTo(genericTypeIndex = 0) Closure<Void> conf) {
    def result = clazz.newInstance()
    result.with(conf)
    result
}

class Person {
    String name
    int age
}

@CompileStatic
void testIt() {
    def p = configure(Person) {
        name = 'Bob'
        age = 42
    }

    println(p)
}

testIt()