Programming in Scala Forum - Scala is not friendly with space, and if-without-else

Articles |
News |
Weblogs |
Books |
Forums

Artima Forums | Articles | Weblogs | Java Answers | News

Sponsored Link •

Programming in Scala Forum
Scala is not friendly with space, and if-without-else

4 replies on 1 page. Most recent reply: Dec 20, 2008 1:36 PM by Seth Tisue

Welcome Guest
Sign In

Back to Topic List

Reply to this Topic

Search Forum

Threaded View


Previous Topic		Next Topic

Flat View: This topic has 4 replies on 1 page

Haixu Huang

Posts: 6
Nickname: regular
Registered: Oct, 2008

Scala is not friendly with space, and if-without-else

Posted: Dec 15, 2008 9:33 PM

For example, if I defined


class A(int u) {
  val unary_=u
  def +(A a) = {new A(unary_+a.unary_)}
  def unary_+(A a) = { a }
}

OK, I confess it's a very badly format. But a language should permit a genius or a dull fish write this kind of code to do some useless thing.

So I think maybe use some magic format to define the operator should be acceptable. For example,


class A(int u) {
  val unary_=u // unary_ is a member of class A
  def {_+_}(A a) = {new A(unary_+a.unary_)}
    // code above defined a plus operator
  def {+_}(A a) = { a }
    // code above defined a prefix unary + operator
  private def factorial(int i) =
  { if (i == 1) 1 else i * factorial(i - 1) }
  def {_!}(A a) = {new A(factorial(unary_))}
    // code above defined a suffix unary ! operator
}

Also, version 6 of Book omited the discuss of difference between


  if (true | false) value

and


  if (true | false) value1 else value2

Does it mean anything? In Scala v 2.7.2, the first one still produce Unit no matter the expression is true or false, will it be changed in next version? Waiting for the answer here.

Alex Cruise

Posts: 3
Nickname: arrgh
Registered: Dec, 2007

Re: Scala is not friendly with space, and if-without-else

Posted: Dec 16, 2008 10:57 AM

> Also, version 6 of Book omited the discuss of difference
> between
> if (true | false) value
> and
> if (true | false) value1 else value2
>
> Does it mean anything? In Scala v 2.7.2, the first one
> still produce Unit no matter the expression is true or
> false, will it be changed in next version? Waiting for the
> answer here.

If you use if as an expression that returns a value, the inferred type of the expression is the least upper bound of the "then" and "else" clauses. Since the else clause doesn't return a value, Unit is the LUB. If you use an if imperatively (e.g. if (condition) mutateMyState()) everything will work as you'd expect because you don't care about the return value anyway.

Alex Cruise

Posts: 3
Nickname: arrgh
Registered: Dec, 2007

Re: Scala is not friendly with space, and if-without-else

Posted: Dec 16, 2008 10:59 AM

Note that some would argue, with some justification, thatval foo = if (cond) value (i.e. without an else clause) should throw an exception.

Haixu Huang

Posts: 6
Nickname: regular
Registered: Oct, 2008

Re: Scala is not friendly with space, and if-without-else

Posted: Dec 16, 2008 8:49 PM

> > Also, version 6 of Book omited the discuss of
> difference
> > between
> > if (true | false) value
> > and
> > if (true | false) value1 else value2
> >
> > Does it mean anything? In Scala v 2.7.2, the first one
> > still produce Unit no matter the expression is true or
> > false, will it be changed in next version? Waiting for
> the
> > answer here.
>
> If you use if as an expression that returns a value, the
> inferred type of the expression is the least upper bound
> of the "then" and "else" clauses. Since the else clause
> doesn't return a value, Unit is the LUB. If you use an if
> imperatively (e.g. if (condition) mutateMyState())
> everything will work as you'd expect because you don't
> care about the return value anyway.

Don't think so.
try this following code in interpretor:


val a = if (true) "a" else ()

the shell will reply:


a: Any = a

I think the only thing needed is "else ()", or maybe "else new Exception", but should be implicited.

Seth Tisue

Posts: 2
Nickname: sethtisue
Registered: Feb, 2008

Re: Scala is not friendly with space, and if-without-else

Posted: Dec 20, 2008 1:36 PM

I don't believe this is a mistake or flaw in the language and I hope it won't be "fixed".

Flat View: This topic has 4 replies on 1 page

Previous Topic

Next Topic


	Web Artima.com