Partial application of curried constructors in Scala

Question

Consider the following:

class A(foo: Int)(bar: Int)(baz: Int)
object A{
    def apply(foo: Int)(bar: Int)(baz: Int) = new A(foo)(bar)(baz)
}

With the apply method I can do the following:

scala> A(1)(2)(3)
res12: Script.A = Script$A@7a6229e9

scala> A(1)_
res13: Int => (Int => Script.A) = <function1>

Why is it that I can't do the following:

scala> new A(1)_
<console>:21: error: missing arguments for constructor A in class A
              new A(1)_
              ^

Am I missing something syntax wise? I thought constructors are meant to be just methods on the class, so they should be lifted to functions when needed (much like the apply method above)

Answer 1

Calling new on the class supposed to create an instance of that class (A in you case), but what you are trying to do with new A(1) _ is to make an instance of A class without complete data for the contractor, which is essentially not logical at all. But writing A(1) _ is correct and logical cause in this case you are lifting a method into a function (apply method from A companion object) which already has all the data to make an instance of that class.