precedence rules are catching you out here, you need the braces:
def x = { val y = 5 }It also works just fine in compiled code On 17 September 2010 17:19, Ricky Clarkson <[email protected]> wrote: > That's an interpreter illusion; a variable declaration is not actually a > value, otherwise you would be able to write: > > def x = val y = 5 > > On Fri, Sep 17, 2010 at 4:50 PM, Kevin Wright <[email protected]>wrote: > >> >> >> >> >> On 17 September 2010 16:18, Reinier Zwitserloot <[email protected]>wrote: >> >>> Correction: In java, as in scala, all expressions "return" a value >>> (not really the right term, that. Expressions *have* a value is closer >>> to the mark). It's just that in scala more things are expressions. >>> Like "if": Expression in scala, statement in java. Not ALL things in >>> scala are expressions. Variable declarations aren't, for example. >>> >> >> Hot from the Scala REPL: >> >> scala> val x = { val y = 32 } >> x: Unit = () >> >> So even variable assignments evaluate to a value. >> >> >>> In any java library that isn't completely worthless, the code is >>> "getField()". If you get annoyed at writing out the accessor, use >>> lombok. Claiming that as a benefit to scala seems like you're grasping >>> for reasons. >>> >> >> It's a major benefit: >> >> trait X { >> def property : Int >> } >> >> class Y extends X { >> val property = 32 >> } >> >> When I use `property` from an object of type X, it really doesn't matter >> if it's implemented via a field of if it's computed. >> That freedom from having to know (or care) is a simplification to me. >> >> >>> A useful definition for "higher level" is that it makes invisible / >>> automated whatever's trivial detail. This is a double-edged knife, >>> though: Whether or not a detail is trivial depends on the problem. For >>> example, C conveniently abstracts away the concept of stack, but in >>> the process of doing so, removes the ability to store stacks. The JVM >>> abstracts away memory management, but in the process of doing so >>> introduces non-determinism due to gc runs. >>> >>> However, with that definition scala isn't much higher than java. There >>> aren't many things that you can no longer do in scala but which you >>> can do in java, and on the flipside, there aren't many things that are >>> orders of magnitude simpler in scala than java because something has >>> been abstracted away. Scala is more a sideways step: It's operating at >>> the same general level of abstraction as java, but with a different >>> syntax, which includes more emphasis on function objects (something >>> java CAN do, but not with particularly nice syntax), as well as a less >>> rigid syntax structure, and a general more functional outlook. >> >> >> Function objects are just a tiny part of it, not only does Scala have >> functions that are objects, but also any arbitrary object can be made into a >> function. >> On top of this there's pattern matching, implicits (which allow for type >> classes), higher-kinded types and by-name params. >> Closures alone don't make a language higher level than Java, but Scala >> really isn't about just closures... >> >> Just compare the implementation of a heterogenous list in both languages: >> >> http://apocalisp.wordpress.com/2008/10/23/heterogeneous-lists-and-the-limits-of-the-java-type-system/ >> >> http://apocalisp.wordpress.com/2010/07/06/type-level-programming-in-scala-part-6a-heterogeneous-list%C2%A0basics/ >> >> >> >>> On Sep 17, 3:28 pm, Kevin Wright <[email protected]> wrote: >>> > I'm recently taking the position that it's impossible to state which of >>> two >>> > languages is "simpler", the term is just too heavily overloaded. >>> > >>> > Just pick your definition and it's trivial to show that assembly is >>> simpler >>> > than LISP, or vice-versa, but you've still achieved nothing. If we use >>> the >>> > term "higher-level" instead of "simpler", then this difficulty >>> evaporates. >>> > >>> > Personally I feel that Scala is simpler than Java, but that statement >>> means >>> > nothing without also explaining the particular definition of the term >>> that >>> > matters to me. In this case, it's two features of that language that >>> really >>> > stand out, and show Scala to be the higher-level language.. >>> > >>> > 1. It has constructs that closely match the way I think about problems. >>> > When I have to mangle the design in my head so that it matches the >>> features >>> > of the target language, I perceive that as an unneccessary complication >>> in >>> > the design+implementation process. >>> > 2. Scala has a smaller general-purpose syntax that I can use accross a >>> wide >>> > range of problems, instead of a larger number special-case constructs. >>> For >>> > example: >>> > >>> > - Java has the ?: operator, but Scala has the much more general idea >>> that >>> > all expressions return a value. >>> > >>> > - Java has a switch statement over numbers, enums and (soon) Strings, >>> wheras >>> > Scala has pattern matching that isn't limited to any type. >>> > >>> > - Java has primitives, and operators are limited to only working with >>> > primitives. Everything in Scala is an object, and operators are just >>> > methods. >>> > >>> > - Java has special behaviour for concatenating an object or primitive >>> to a >>> > string, Scala can do this with implicit conversions - a feature that's >>> > useful in many more situations. >>> > >>> > - To fetch a value from an object in Java, I must first know if it's a >>> fixed >>> > value or if it'll be calculated, and so use field or getField() as >>> > appropriate, Scala doesn't force this distinction and so it's enough to >>> know >>> > I'm fetching a value, the underlying logic could even be changed in the >>> > future without breaking my code. >>> > >>> > The ability to work with general concepts and not have to chose exactly >>> > which special feature I need in a given situation... I see that as >>> > simplifying the task of programming. >>> > I could say more, but it's probably just "simpler" to point here: >>> http://stackoverflow.com/questions/727078/whats-so-great-about-scala/... >>> > >>> > On 17 September 2010 11:30, Reinier Zwitserloot <[email protected]> >>> wrote: >>> > >>> > >>> > >>> > > That just sounds like equating "simple" to "less verbose". >>> > >>> > > For example, with optional () for args-less method calls, you get a >>> > > number of things which one might deem "simpler": >>> > >>> > > - Less characters to type and read >>> > > - The ability to not have to care about whether the doClick member >>> is >>> > > a method or a field >>> > >>> > > On the other hand, you also get a few things which are decidedly more >>> > > complicated: >>> > >>> > > - A stylistic choice about whether or not you add the (). Having to >>> > > make an irrelevant choice of any sort clearly seems like a lack of >>> > > simplicity to me. >>> > > - The INability to tell if doClick is a field or a method. In >>> certain >>> > > circumstances it matters, and having to look it up is more >>> complicated >>> > > than being able to tell at a casual glance. >>> > >>> > > These are clearly conflicting requirements. Forcing you to care >>> > > whether doClick is a field or a method is needless complexity.... >>> > > unless it isn't, in which case not being able to tell is needless >>> > > complexity. Offering the programmer the choice doesn't help, because >>> > > the choice in it self is needless complexity, and by existing we >>> still >>> > > can't tell, given "foo.doClick", if doClick is a field or a method. >>> > > We'd have to rely on a programmer following the local style >>> guidelines >>> > > (if, say, these state that non-fields ought to be called with >>> parens), >>> > > which you can' even unit test. Now we're introducing needless >>> > > complexity there. >>> > >>> > > Oh, how complicated. >>> > >>> > > There's also the issue of moving complexity around to the problem >>> > > domain. My usual retort to those complaining about the complexity of >>> > > generics is simply this: Co- and Contravariance is _inherently_ >>> > > complicated. When you have a problem where generics is required or >>> > > seems quite useful, then the problem has this complexity, inherently. >>> > > You can choose not to use generics, but then the complexity is just >>> > > hidden away in javadocs and a bunch of casts. You can tweak generics >>> a >>> > > bit, declaration-site generics probably being the most drastic, but a >>> > > truly "simple" generics will never be, because co/contravariance >>> isn't >>> > > simple. >>> > >>> > > So, did java become more complex when 1.5 was introduced? Yes. Does >>> > > this mean java 1.5 is worse than 1.4? No - in fact, it's better. >>> > >>> > > So, in certain ways, a more complex language is actually a good >>> thing. >>> > >>> > > Hence my conclusion that all this talk about "complexity" is not >>> going >>> > > to convince anybody one way or another, because its very very easy >>> for >>> > > anyone reading the word "complexity" and imagine whatever situation >>> is >>> > > least likely to convince them. >>> > >>> > > So, to try and mitigate this, here's where I believe scala has added >>> > > needless complexity: >>> > >>> > > Stylistic choice is EVERYWHERE. This is what, as I said, *I* mean by >>> > > DSLish features (yet another vague term that can mean just about >>> > > anything). Should I put () after an args-less method call? There's a >>> > > stylistic choice there. dots to dereference? Another stylistic >>> choice. >>> > > Use operator overloading, or not, and if I do, left-associative or >>> > > right-associative? There's also boatloads of semantic choice in >>> scala. >>> > > If I need to iterate over a map and, say, produce a list containing >>> > > the concatenation of each key and associated value, in java there's >>> > > really only two obvious ways to do it. Both involve looping, and the >>> > > only difference is whether I iterator over entrySet() or keySet(). In >>> > > scala, there's _way_ more choices. I can do a java-style loop, or I >>> > > can use an each construct that fills the list, or I can turn the keys >>> > > and the values into two sets, and then zip them up, functional style, >>> > > or I could use a comprehension of some sort. >>> > >>> > > Why is this bad: >>> > >>> > > Well, obviously a language can't eliminate _all_ stylistic choice. At >>> > > the very least you have to pick a name for your methods, and naming >>> is >>> > > clearly up to you, the API author. But, scala goes _way_ too far in >>> my >>> > > opinion. While it seems like a nice idea, give an API designer, and >>> an >>> > > API user, the ability to write in whatever feels most natural (i.e. >>> > > readable, easy to maintain), that's great! Except when it isn't: By >>> > > introducing all these stylistic choices, you're forcing the API user >>> > > to pick at every stage. Sometimes, this choice is good, because the >>> > > benefits of picking the best option available outweigh the burden of >>> > > having the choice. In all other situations, though, this choice is >>> not >>> > > useful at all. It makes sharing code harder (because Joe likes >>> 'each', >>> > > but Jack likes 'for'). This is like spaces v. tabs: The flexibility >>> of >>> > > using either really isn't helping. We'd have been better off if back >>> > > in the day someone put their foot down and declared some indent style >>> > > to be the only one compilers will accept from here on out. Deviation >>> > > from this one rule results in compiler warnings. I can't claim to be >>> > > very scientific about it, but to me it feels like Scala has gone >>> > > waaaay too far down the "give the programmers the flexibility" path. >>> > > Where the flexibility helps me make code do different things, that's >>> > > fantastic. Where this flexibility boils down to the exact same end >>> > > result, and I just have many different ways of expressing the same >>> > > concept, usually, it's just a bother. It's needless complication. >>> > >>> > > The python folks differentiated themselves from the Perl folks early >>> > > by turning Larry Wall's "There Are Many Ways To Do It" around into >>> > > "There Is Only One Way To Do It" and I subscribe to the theory. >>> > > Introducing stylistic choice needlessly is always bad. But yet again >>> > > there's a dichotomy here: Where stylistic choice turns from pointless >>> > > to useful is a moving target, there isn't a single answer to the >>> > > question. >>> > >>> > > Perhaps I was unclear about my comment in regards to using java >>> > > libraries in scala code: If you're going to write scala, then... >>> write >>> > > scala. Which means you use THEIR collection APIs. If you stick with >>> > > java.util.List, then interopping with other scala code is going to be >>> > > a nightmare, and even if most scala programmers are familiar with the >>> > > java APIs (which is clearly an argument that can't scale: If scala >>> > > outgrows java in popularity, or gets even remotely close to it, how >>> > > can that possibly be true?), its like not following the camelcasing >>> > > conventions in java code. It throws people off, makes your code >>> > > ridiculously hard to understand. Just don't do it. There's no going >>> > > halfway, and there's not much point (as you said too) in trying to >>> > > stay up to date with both java and scala. Pick one. That's your go-to >>> > > language for larger projects where static typing is nice, and/or >>> speed >>> > > is not unimportant. If you want to learn more languages, fantastic. >>> > > But don't pick java and scala. That's a silly combination, the >>> problem >>> > > domains where these 2 languages shine overlap far too much. >>> > >>> > > On Sep 17, 10:42 am, Ricky Clarkson <[email protected]> >>> wrote: >>> > > > Reinier, >>> > >>> > > > You want a definition of simple? Ok, some code is more simple than >>> some >>> > > > other code if it contains fewer tokens that are outside the domain. >>> > > E.g., >>> > > > Cobol's ADD 1 TO AGE GIVING AGE is not as simple as C's age++. >>> Java's >>> > > > SwingUtilities.invokeLater(new Runnable() { public void run() { >>> > > > button.doClick(); } }) is not as simple as Scala's: >>> > > doLater(button.doClick). >>> > >>> > > > Staying cutting edge on Scala is easier as it does not require a >>> cutting >>> > > > edge runtime. >>> > >>> > > > In my opinion, for tasks for which Java is a reasonable option, so >>> is >>> > > Scala, >>> > > > as it is typed and runs in the same environment. I wouldn't look >>> at >>> > > Groovy, >>> > > > JRuby or Jython for those, because they are untyped. >>> > >>> > > > Regarding writing in DSLs, pretty much all code unless >>> > >>> > ... >>> > >>> > read more » >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "The Java Posse" group. >>> To post to this group, send email to [email protected]. >>> To unsubscribe from this group, send email to >>> [email protected]<javaposse%[email protected]> >>> . >>> For more options, visit this group at >>> http://groups.google.com/group/javaposse?hl=en. >>> >>> >> >> >> -- >> Kevin Wright >> >> mail / gtalk / msn : [email protected] >> pulse / skype: kev.lee.wright >> twitter: @thecoda >> >> -- >> You received this message because you are subscribed to the Google Groups >> "The Java Posse" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]<javaposse%[email protected]> >> . >> For more options, visit this group at >> http://groups.google.com/group/javaposse?hl=en. >> > > -- > You received this message because you are subscribed to the Google Groups > "The Java Posse" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]<javaposse%[email protected]> > . > For more options, visit this group at > http://groups.google.com/group/javaposse?hl=en. > -- Kevin Wright mail / gtalk / msn : [email protected] pulse / skype: kev.lee.wright twitter: @thecoda -- You received this message because you are subscribed to the Google Groups "The Java Posse" group. 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