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Annotation 149632564

#scala

When a function value containing a return statement is evaluated nonlocally, the computation is abandoned and the result is returned by throwing a NonLocalReturnControl[A].

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tpolecat
it returns from the method it appears in. Another example: def foo: Int = { val sumR: List[Int] => Int = _.foldLeft(0)((n, m) => return n + m) sumR(List(1,2,3)) + sumR(List(4,5,6)) } scala> foo res4: Int = 1 Non-Local Return <span>When a function value containing a return statement is evaluated nonlocally, the computation is abandoned and the result is returned by throwing a NonLocalReturnControl[A]. This implementation detail escapes into the wild without much ceremony: def lazily(s: => String): String = try s catch { case t: Throwable => t.toString } def foo: String = laz

Annotation 149632571

#scala

calling return in Scala is like invoking the continuation in Scheme

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tpolecat
ype) you know that the expression has no normal form; when evaluated it must loop forever, exit the VM, or (behind door #3) abruptly pass control elsewhere, which is what's happening here. If your reaction is "well logically you're just <span>invoking the continuation, which we totally do all the time in Scheme so I don't see the problem" then fine. Cookie for you. The rest of us think it's insane. Return is not referentially transparent. This kind of goes without saying, but just in case you're not sure what thi

Annotation 149632582

#scala

whenever you encounter an expression of type Nothing: because Nothing is uninhabited (there are no values of that type) you know that the expression has no normal form; when evaluated it must (one of):

loop forever
exit the VM
abruptly pass control elsewhere (use return or throw exception?)

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tpolecat
What's going on? Whatever the type of return 2 is, it comforms with both Int and String. And since both of those classes are final and Int is an AnyVal you know where this is headed. def x: Int = { val a: Nothing = return 2; 1 } Right. So, <span>whenever you encounter an expression of type Nothing you would do well to turn smartly and head the other direction. Because Nothing is uninhabited (there are no values of that type) you know that the expression has no normal form; when evaluated it must loop forever, exit the VM, or (behind door #3) abruptly pass control elsewhere, which is what's happening here. If your reaction is "well logically you're just invoking the continuation, which we totally do all the time in Scheme so I don't see the problem" then fine. Cookie for you.

Annotation 149632603

#odersky-programming-in-scala-2ed #scala

Scala’s on-demand imports are written with a trailing underscore (_) instead of an asterisk (*) like in Java.

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Flashcard 149632614

Tags

#odersky-programming-in-scala-2ed #scala

Question

if we have:


abstract class Fruit(
  val name: String,
  val color: String
)

what does import fruit._ mean?


def showFruit(fruit: Fruit) {
  import fruit._
  // rest of the method
}

Answer

you can use name and color (fields from Fruit) directly:
println(name +"s are "+ color)

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Flashcard 149632625

Tags

#odersky-programming-in-scala-2ed #scala

Question

What does it mean?
import Fruits.{Apple, Orange}

Answer

importing only 2 names from Fruits

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Flashcard 149632636

Tags

#odersky-programming-in-scala-2ed #scala

Question

What does it mean?
import Fruits.{Apple => McIntosh, Orange}

Answer

This imports the two members Apple and Orange from object Fruits.
However, the Apple object is renamed to McIntosh.

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Flashcard 149632647

Tags

#odersky-programming-in-scala-2ed #scala

Question

How can I refer to java.sql.Date class if I use this in Scala?
import java.{sql => S}

Answer

S.Date

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Flashcard 149632658

Tags

#odersky-programming-in-scala-2ed #scala

Question

What's the other way of writing
import Fruits._
in full, using import selector?

Answer

import Fruits.{_}

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Flashcard 149632669

Tags

#odersky-programming-in-scala-2ed #scala

Question

How to import everything from Fruits but rename Apple to McIntosh?

Answer

import Fruits.{Apple => McIntosh, _}

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Flashcard 149632680

Tags

#odersky-programming-in-scala-2ed #scala

Question

How to import everything except for Pear (i.e. exclude Pear) from Fruits?

Answer

import Fruits.{Pear => _, _}

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Flashcard 149632691

Tags

#odersky-programming-in-scala-2ed #scala

Question

How can I write import p.n using full import selectors?

Answer

import p.{n}

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Annotation 149632706

#odersky-programming-in-scala-2ed #scala

The implicit imports in every Scala program are:

import java.lang._
import scala._
import Predef._

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Flashcard 149632715

Tags

#odersky-programming-in-scala-2ed #scala

Question

The implicit imports in every Scala program are:

[...]
import scala._
import Predef._

Answer

import java.lang._

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Parent (intermediate) annotation

Open it
The implicit imports in every Scala program are: import java.lang._ import scala._import Predef._

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Flashcard 149632722

Tags

#odersky-programming-in-scala-2ed #scala

Question

The implicit imports in every Scala program are:

import java.lang._
[...]
import Predef._

Answer

import scala._

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Parent (intermediate) annotation

Open it
The implicit imports in every Scala program are: import java.lang._ import scala._import Predef._

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Flashcard 149632729

Tags

#odersky-programming-in-scala-2ed #scala

Question

The implicit imports in every Scala program are:

import java.lang._
import scala._
[...]

Answer

import Predef._

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Parent (intermediate) annotation

Open it
The implicit imports in every Scala program are: import java.lang._ import scala._import Predef._

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Flashcard 149632747

Tags

#odersky-programming-in-scala-2ed #scala

Question


class Outer {
 class Inner {
  private def f() { println("f") }
  class InnerMost {
   f()
  }
 }
 (new Inner).f() // is it legal in Scala? why? woudl it be legal in Java?
}

Answer

access (new Inner).f() is illegal because f is declared private in Inner and the access is not from within class Inner - in Java it would be legal

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Flashcard 149632756

Tags

#odersky-programming-in-scala-2ed #scala

Question


class Outer {
 class Inner {
  private def f() { println("f") }
  class InnerMost {
   f() // is it legal in Scala? why? would it be legal in Java?
  }
 }
 (new Inner).f() // warning - illegal!
}

Answer

Yes. In both languages. A inner class accessing private member of the class it is declared in.

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Flashcard 149632767

Tags

#odersky-programming-in-scala-2ed #scala

Question

In Java protected members are accessible from subclasses and within the same package. How is it in Scala?

Answer

only accessible from subclasses

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Flashcard 149632778

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#odersky-programming-in-scala-2ed #scala

Question

Every member not labeled private or protected is [...].

Answer

implicitely public

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Flashcard 149632789

Tags

#odersky-programming-in-scala-2ed #scala

Question

What does access modifier private[this] mean? Is it more or less restrictive than private ?

Answer

It is more restrictive, because it allows access only from the same object. Same class, different object is not allowed (think: typical implementation of equals() in Java has this.x == that.x; it wouldn't work with private[this] in Scala)

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Flashcard 149632800

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#odersky-programming-in-scala-2ed #scala

Question

How to create package object for a package rocket ?

Answer


package object rocket {
  // definitions go here
}

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Flashcard 149632811

Tags

#odersky-programming-in-scala-2ed #scala

Question

What do you put into package objects? How is it different than Java?

Answer

Any kind of definition that you can put inside a class, you can also put at the top level of a package, by putting it into package object. In Java, only classes and interfaces can be members of packages.

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Edited, memorised or added to reading queue

on 08-Sep-2014 (Mon)

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Parent (intermediate) annotation

Original toplevel document (pdf)

Parent (intermediate) annotation

Original toplevel document (pdf)

Parent (intermediate) annotation

Original toplevel document (pdf)

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