在 Scala 中创建新对象后的代码块

Question

I have a constructor defined as

class Test{ var i = 0; println("constructor"); }

And I call it as

val t = new Test { println("codeblock"); i = 7; }

The result of this is:

constructor
codeblock
defined class Test
t: Test = $anon$1@4a7b4f79
res3: Int = 7

So I see that the code block on the same line as new is executed as if it was part of the constructor. I am not familiar with this.

Could some one clarify this behaviour and/or point to reference that explains the semantics at play here? I am not sure how to google this - looking for code block on same line as constructor call scala doesn'y help much.

Answer 1

It's roughly equivalent to this:

class Test{ var i = 0; println("constructor"); }

class TestImpl extends Test {
  println("codeblock")
  i = 7
}

scala> new TestImpl
constructor
codeblock
res8: TestImpl = TestImpl@6baf697c

scala> res8.i
res9: Int = 7

So you can see that initialization order comes from more abstract to a more concrete class.

To highlight @som-snytt's comment pointing to Scala Language Specification: general instance creation expression