Private constructor in Kotlin

Question

In Java it's possible to hide a class' main constructor by making it private and then accessing it via a public static method inside that class:

public final class Foo {     /* Public static method */     public static final Foo constructorA() {         // do stuff          return new Foo(someData);     }      private final Data someData;      /* Main constructor */     private Foo(final Data someData) {         Objects.requireNonNull(someData);          this.someData = someData;     }      // ... } 

How can the same be reached with Kotlin without separating the class into a public interface and a private implementation? Making a constructor private leads to it not being accessible from outside the class, not even from the same file.

Answer 1

You can even do something more similar to "emulating" usage of public constructor while having private constructor.

class Foo private constructor(val someData: Data) {     companion object {         operator fun invoke(): Foo {             // do stuff              return Foo(someData)         }     } }  //usage Foo() //even though it looks like constructor, it is a function call