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I've been curious about the impact of not having an explicit primary constructor in Scala, just the contents of the class body.
In particular, I suspect that the private or protected constructor pattern, that is, controlling construction through the companion object or another class or object's methods might not have an obvious implementation.
Am I wrong? If so, how is it done?
959
No, Constructors can be public , private , protected or default (no access modifier at all). Making something private doesn't mean nobody can access it. It just means that nobody outside the class can access it. So private constructor is useful too.
A protected constructor means that only derived members can construct instances of the class (and derived instances) using that constructor. This sounds a bit chicken-and-egg, but is sometimes useful when implementing class factories.
In Scala, only a primary constructor is allowed to invoke a superclass constructor. In Scala, we are allowed to make a primary constructor private by using a private keyword in between the class name and the constructor parameter-list.
There are two types of constructor in Scala – Primary and Auxiliary. Not a special method, a constructor is different in Scala than in Java constructors. The class' body is the primary constructor and the parameter list follows the class name.
You can declare the default constructor as private/protected by inserting the appropriate keyword between the class name and the parameter list, like this:
class Foo private () { /* class body goes here... */ } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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