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    <p>You can use <code>lazy val</code>:</p> <pre><code>scala&gt; :paste // Entering paste mode (ctrl-D to finish) case class Person (val name: String, val surname: String) case class Family (val nameFamily: String, val members: Set[Person]) lazy val f1 = new Family ("Red", Set(p1, p2)) lazy val p1 = new Person ("John", "Smith") lazy val p2 = new Person ("Luis", "Smith") // Exiting paste mode, now interpreting. defined class Person defined class Family f1: Family = &lt;lazy&gt; p1: Person = &lt;lazy&gt; p2: Person = &lt;lazy&gt; scala&gt; f1 res0: Family = Family(Red,Set(Person(John,Smith), Person(Luis,Smith))) </code></pre> <p>If you want to set some value somewhere after creation of object only once you should use Promise from scala 2.10:</p> <pre><code>import concurrent.{Promise, Future} case class Person (val name: String, val surname: String) class Family (val nameFamily: String) { private val membersPromice = Promise[Set[Person]] def setMembers(m: Set[Person]) { membersPromice.success(m) } val membersFuture = membersPromice.future def members = membersFuture.value.map(_.get) override def toString() = "Family(" + nameFamily + ", " + members.getOrElse("&lt;future&gt;") + ")" } </code></pre> <p>Usage:</p> <pre><code>scala&gt; val f = new Family("red") f: Family = Family(red, &lt;future&gt;) scala&gt; val (p1, p2) = (Person("John", "Smith"), Person("Luis", "Smith")) p1: Person = Person(John,Smith) p2: Person = Person(Luis,Smith) scala&gt; f.setMembers(Set(p1, p2)) scala&gt; f res1: Family = Family(red, Set(Person(John,Smith), Person(Luis,Smith))) scala&gt; f.setMembers(Set(p1, p2)) java.lang.IllegalStateException: Promise already completed. </code></pre> <p>You can use <a href="https://web.archive.org/web/20120513085210/http://www.tikalk.com/java/blog/type-safe-builder-scala-using-type-constraints" rel="nofollow noreferrer">type-safe builder pattern</a>:</p> <pre><code>case class Person (val name: String, val surname: String) case class Family (val nameFamily: String, val members: Set[Person]) sealed abstract class TBool class TTrue extends TBool class TFalse extends TBool class FamilyBuilder[WithName &lt;: TBool, WithMembers &lt;: TBool](val nameFamily: Option[String], val members: Option[Set[Person]]) { def withName(nameFamily: String)(implicit i: WithName =:= TFalse) = new FamilyBuilder[TTrue, WithMembers](Some(nameFamily), members) def withMembers(members: Set[Person])(implicit i: WithMembers =:= TFalse) = new FamilyBuilder[WithName, TTrue](nameFamily, Some(members)) def create()(implicit i1: WithName =:= TTrue, i2: WithMembers =:= TTrue) = Family(nameFamily.get, members.get) } object FamilyBuilder { def apply() = new FamilyBuilder[TFalse, TFalse](None, None) } </code></pre> <p>Usage:</p> <pre><code>scala&gt; FamilyBuilder() withName "Red" withMembers Set(p1, p2) create() res1: Family = Family(Red,Set(Person(John,Smith), Person(Luis,Smith))) scala&gt; FamilyBuilder() withMembers Set(p1, p2) withName "Red" create() res2: Family = Family(Red,Set(Person(John,Smith), Person(Luis,Smith))) scala&gt; FamilyBuilder() withName "Red" create() &lt;console&gt;:1: error: Cannot prove that TFalse =:= TTrue. FamilyBuilder() withName "Red" create() ^ </code></pre>
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    1. POScala: initialize fields with instances created later
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    1. COI can only use the variables lazy in the main. There is a solution to be applied in the model of domain, on the declaration of the class.
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    2. COI've updated my answer. Is it what you are looking for?
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    3. COHi, thanks for the answer, but it is not what I'm looking. I have updated my problem.
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