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  • trait implementation

    - by Jeriho
    If I have some traits like: trait A {...} trait B extends A{...} trait C1 extends B{...} trait C2 extends A{...} I can write class in two ways (C1 and C2 add same functionality) class Concrete1 extends B with C1 class Concrete2 extends B with C2 What variant is better(efficient)?

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  • Trait, FunctionN, or trait-inheriting-FunctionN in Scala?

    - by Willis Blackburn
    I have a trait in Scala that has a single method. Call it Computable and the single method is compute(input: Int): Int. I can't figure out whether I should Leave it as a standalone trait with a single method. Inherit from (Int = Int) and rename "compute" to "apply." Just get rid of Computable and use (Int = Int). A factor in favor of it being a trait is that I could usefully add some additional methods. But of course if they were all implemented in terms of the compute method then I could just break them out into a separate object. A factor in favor of just using the function type is simplicity and the fact that the syntax for an anonymous function is more concise than that for an anonymous Computable instance. But then I've no way to distinguish objects that are actually Computable instances from other functions that map Int to Int but aren't meant to be used in the same context as Computable. How do other people approach this type of problem? No right or wrong answers here; I'm just looking for advice.

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  • C++: get const or non-const reference type from trait

    - by maciekp
    I am writing a functor F which takes function of type void (*func)(T) and func's argument arg. Then functor F calls func with arg. I would like F not to copy arg, just to pass it as reference. But then I cannot simply write "void F(void (*func)(T), T&)" because T could be a reference. So I am trying to write a trait, which allows to get proper reference type of T: T -> T& T& -> T& const T -> const T& const T& -> const T& I come up with something like this: template<typename T> struct type_op { typedef T& valid_ref_type; }; template<typename T> struct type_op<T&> { typedef typename type_op<T>::valid_ref_type valid_ref_type; }; template<typename T> struct type_op<const T> { typedef const T& valid_ref_type; }; template<typename T> struct type_op<const T&> { typedef const T& valid_ref_type; }; Which doesn't work for example for void a(int x) { std::cout << x << std::endl; } F(&a, 7); Giving error: invalid initialization of non-const reference of type ‘int&’ from a temporary of type ‘int’ in passing argument 2 of ‘void f(void (*)(T), typename type_op::valid_ref_type) [with T = int]’ How to get this trait to work?

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  • What's the most important trait of a programmer desired by peer programmers [closed]

    - by greengit
    Questions here talk about most important programming skills someone is supposed to possess, and, a lot of great answers spring up. The answers and the questioners seem mostly interested on qualities related to getting a better job, nailing some interview, things desired by boss or management, or improving your programming abilities. One thing that often gets blown over is the genuine consideration for what traits peers want. They don't much value things like you're one of those 'gets things done' people for the company, or you never miss a deadline, or your code is least painful to review and debug, or you're team player with fantastic leading abilities. They probably care more if you're helpful, are a refreshing person to talk to, you're fun to program in pair with, everybody wants you to review their code, or something of that nature. I, for one, would care that I come off to my peers as a pleasurable programmer to work with, as much as I care about my impression on my boss or management. Is this really significant, and if yes, what are the most desirable traits peers want from each other.

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  • Avoiding NPE in trait initialization without using lazy vals

    - by 0__
    This is probably covered by the blog entry by Jesse Eichar—still I can't figure out how to correct the following without residing to lazy vals so that the NPE is fixed: Given trait FooLike { def foo: String } case class Foo( foo: String ) extends FooLike trait Sys { type D <: FooLike def bar: D } trait Confluent extends Sys { type D = Foo } trait Mixin extends Sys { val global = bar.foo } First attempt: class System1 extends Mixin with Confluent { val bar = Foo( "npe" ) } new System1 // boom!! Second attempt, changing mixin order class System2 extends Confluent with Mixin { val bar = Foo( "npe" ) } new System2 // boom!! Now I use both bar and global very heavily, and therefore I don't want to pay a lazy-val tax just because Scala (2.9.2) doesn't get the initialisation right. What to do?

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  • Accessing type-parameter of a type-parameter

    - by itemState
    i would like to access, in a trait, the type-parameter of a type-parameter of that trait. without adding this "second-order" type-parameter as another "first-order" parameter to the trait. the following illustrates this problem: sealed trait A; sealed trait A1 extends A; sealed trait A2 extends A trait B[ ASpecific <: A ] { type ASpec = ASpecific } trait D[ ASpecific <: A ] extends B[ ASpecific ] trait C[ +BSpecific <: B[ _ <: A ]] { def unaryOp : C[ D[ BSpecific#ASpec ]] } def test( c: C[ B[ A1 ]]) : C[ D[ A1 ]] = c.unaryOp the test fails to compile because apparently, the c.unaryOp has a result of type C[D[A]] and not C[D[A1]], indicating that ASpec is merely a shortcut for _ <: A and does not refer to the specific type parameter. the two-type-parameter solution is simple: sealed trait A; sealed trait A1 extends A; sealed trait A2 extends A trait B[ ASpecific <: A ] trait D[ ASpecific <: A ] extends B[ ASpecific ] trait C[ ASpecific <: A, +BSpecific <: B[ ASpecific ]] { def unaryOp : C[ ASpecific, D[ ASpecific ]] } def test( c: C[ A1, B[ A1 ]]) : C[ A1, D[ A1 ]] = c.unaryOp but i don't understand why i need to clutter my source with this second, obviously redundant, parameter. is there no way to retrieve it from trait B?

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  • Mixin or Trait implementation in AS3?

    - by Brian Heylin
    I'm looking for ideas on how to implement a Mixin/Trait style system in AS3. I want to be able to compose a number of classes together into a single object. Of course this is not a language level feature of AS3, but I'm hoping that there is maybe some way to do this using prototype based techniques or maybe some bytecode hacking that I believe AsMock uses to implement it's functionality. An existing Java example is Qi4J where the user define interfaces that the Qi4j framework implements based on metadata tags and coding by convention. Has anyone any ideas on how to get the Mixin/Trait concept working within AS3?

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  • Simulate stochastic bipartite network based on trait values of species - in R

    - by Scott Chamberlain
    I would like to create bipartite networks in R. For example, if you have a data.frame of two types of species (that can only interact across species, not within species), and each species has a trait value (e.g., size of mouth in the predator allows who gets to eat which prey species), how do we simulate a network based on the traits of the species (that is, two species can only interact if their traits overlap in values for instance)? UPDATE: Here is a minimal example of what I am trying to do. 1) create phylogenetic tree; 2) simulate traits on the phylogeny; 3) create networks based on species trait values. # packages install.packages(c("ape","phytools")) library(ape); library(phytools) # Make phylogenetic trees tree_predator <- rcoal(10) tree_prey <- rcoal(10) # Simulate traits on each tree trait_predator <- fastBM(tree_predator) trait_prey <- fastBM(tree_prey) # Create network of predator and prey ## This is the part I can't do yet. I want to create bipartite networks, where ## predator and prey interact based on certain crriteria. For example, predator ## species A and prey species B only interact if their body size ratio is ## greater than X.

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  • Scala: getting the name of the class the trait is mixed in

    - by Alexey Romanov
    Given an instance of a class, we can obviously return its name: trait MixedInClassDiscovery { val className = this.getClass.getName } class AClass extends MixedInClassDiscovery { ... this.className // returns "AClass" ... } But this way uses reflection, once for every instance of AClass. Can the same be done once for every class, instead? One solution which comes to mind is to mix it into companion objects instead of classes themselves.

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  • Unit testing several implementation of the same trait/interface

    - by paradigmatic
    I program mostly in scala and java, using scalatest in scala and junit for unit testing. I would like to apply the very same tests to several implementations of the same interface/trait. The idea is to verify that the interface contract is enforced and to check Liskov substitution principle. For instance, when testing implementations of lists, tests could include: An instance should be empty, if and only if and only if it has zero size. After calling clear, the size sould be zero. Adding an element in the middle of a list, will increment by one the index of rhs elements. etc. What are the best practices ?

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  • When is @uncheckedVariance needed in Scala, and why is it used in GenericTraversableTemplate?

    - by retronym
    @uncheckedVariance can be used to bridge the gap between Scala's declaration site variance annotations and Java's invariant generics. scala import java.util.Comparator import java.util.Comparator scala trait Foo[T] extends Comparator[T] defined trait Foo scala trait Foo[-T] extends Comparator[T] :5: error: contravariant type T occurs in invariant position in type [-T]java.lang.Object with java.util.Comparator[T] of trait Foo trait Foo[-T] extends Comparator[T] ^ scala import annotation.unchecked._ import annotation.unchecked._ scala trait Foo[-T] extends Comparator[T @uncheckedVariance] defined trait Foo This says that java.util.Comparator is naturally contra-variant, that is the type parameter T appears in parameters and never in a return type. Which begs the question, why is it also used in the Scala collections library: trait GenericTraversableTemplate[+A, +CC[X] <: Traversable[X]] extends HasNewBuilder[A, CC[A] @uncheckedVariance] What are the valid uses for this annotation?

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  • EMERGENCY - Major Problems After Perl Module Installed via WHM

    - by Russell C.
    I attempted to install the perl module Net::Twitter::Role::API::Lists using WHM and after doing so my whole site came down. It seems that something that was updated with the install isn't functioning correctly and since our website it written in Perl none of our site scripts will run. In almost 8 years of working with Perl I've never had any issues arise after installing a perl module so I have no idea how to even start troubleshooting. The error I see when trying to compile any of our Perl scripts is below. I'd appreciate any advice on what might be wrong and steps on how I can go about resolve it. Thanks in advance for your help! Attribute (+type_constraint) of class MooseX::AttributeHelpers::Counter has no associated methods (did you mean to provide an "is" argument?) at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Attribute.pm line 551 Moose::Meta::Attribute::_check_associated_methods('Moose::Meta::Attribute=HASH(0x9ae35b4)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Class.pm line 303 Moose::Meta::Class::add_attribute('Moose::Meta::Class=HASH(0xa4d7718)', 'Moose::Meta::Attribute=HASH(0x9ae35b4)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 142 Moose::Meta::Role::Application::ToClass::apply_attributes('Moose::Meta::Role::Application::ToClass=HASH(0xa4dfb38)', 'Moose::Meta::Role=HASH(0xa3dbdec)', 'Moose::Meta::Class=HASH(0xa4d7718)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application.pm line 72 Moose::Meta::Role::Application::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa4dfb38)', 'Moose::Meta::Role=HASH(0xa3dbdec)', 'Moose::Meta::Class=HASH(0xa4d7718)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 31 Moose::Meta::Role::Application::ToClass::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa4dfb38)', 'Moose::Meta::Role=HASH(0xa3dbdec)', 'Moose::Meta::Class=HASH(0xa4d7718)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role.pm line 419 Moose::Meta::Role::apply('Moose::Meta::Role=HASH(0xa3dbdec)', 'Moose::Meta::Class=HASH(0xa4d7718)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 132 Moose::Util::_apply_all_roles('Moose::Meta::Class=HASH(0xa4d7718)', 'undef', 'MooseX::AttributeHelpers::Trait::Counter') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 86 Moose::Util::apply_all_roles('Moose::Meta::Class=HASH(0xa4d7718)', 'MooseX::AttributeHelpers::Trait::Counter') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose.pm line 57 Moose::with('Moose::Meta::Class=HASH(0xa4d7718)', 'MooseX::AttributeHelpers::Trait::Counter') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Exporter.pm line 293 Moose::with('MooseX::AttributeHelpers::Trait::Counter') called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 10 require MooseX/AttributeHelpers/Counter.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers.pm line 23 MooseX::AttributeHelpers::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/AttributeHelpers.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute/Role/Meta/Class.pm line 6 MooseX::ClassAttribute::Role::Meta::Class::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/ClassAttribute/Role/Meta/Class.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute.pm line 11 MooseX::ClassAttribute::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/ClassAttribute.pm called at /usr/lib/perl5/site_perl/5.8.8/Olson/Abbreviations.pm line 6 Olson::Abbreviations::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require Olson/Abbreviations.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTime/ButMaintained.pm line 10 MooseX::Types::DateTime::ButMaintained::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/Types/DateTime/ButMaintained.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTimeX.pm line 9 MooseX::Types::DateTimeX::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/Types/DateTimeX.pm called at /usr/lib/perl5/site_perl/5.8.8/Net/Amazon/S3/Client/Bucket.pm line 5 Net::Amazon::S3::Client::Bucket::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require Net/Amazon/S3/Client/Bucket.pm called at /usr/lib/perl5/site_perl/5.8.8/Net/Amazon/S3.pm line 111 Net::Amazon::S3::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require Net/Amazon/S3.pm called at /home/atrails/www/cgi-bin/main.pm line 1633 main::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require main.pm called at /home/atrails/cron/meetup.pl line 20 main::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 Attribute (+default) of class MooseX::AttributeHelpers::Counter has no associated methods (did you mean to provide an "is" argument?) at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Attribute.pm line 551 Moose::Meta::Attribute::_check_associated_methods('Moose::Meta::Attribute=HASH(0xa4df4b4)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Class.pm line 303 Moose::Meta::Class::add_attribute('Moose::Meta::Class=HASH(0xa4d7718)', 'Moose::Meta::Attribute=HASH(0xa4df4b4)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 142 Moose::Meta::Role::Application::ToClass::apply_attributes('Moose::Meta::Role::Application::ToClass=HASH(0xa4dfb38)', 'Moose::Meta::Role=HASH(0xa3dbdec)', 'Moose::Meta::Class=HASH(0xa4d7718)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application.pm line 72 Moose::Meta::Role::Application::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa4dfb38)', 'Moose::Meta::Role=HASH(0xa3dbdec)', 'Moose::Meta::Class=HASH(0xa4d7718)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 31 Moose::Meta::Role::Application::ToClass::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa4dfb38)', 'Moose::Meta::Role=HASH(0xa3dbdec)', 'Moose::Meta::Class=HASH(0xa4d7718)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role.pm line 419 Moose::Meta::Role::apply('Moose::Meta::Role=HASH(0xa3dbdec)', 'Moose::Meta::Class=HASH(0xa4d7718)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 132 Moose::Util::_apply_all_roles('Moose::Meta::Class=HASH(0xa4d7718)', 'undef', 'MooseX::AttributeHelpers::Trait::Counter') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 86 Moose::Util::apply_all_roles('Moose::Meta::Class=HASH(0xa4d7718)', 'MooseX::AttributeHelpers::Trait::Counter') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose.pm line 57 Moose::with('Moose::Meta::Class=HASH(0xa4d7718)', 'MooseX::AttributeHelpers::Trait::Counter') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Exporter.pm line 293 Moose::with('MooseX::AttributeHelpers::Trait::Counter') called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 10 require MooseX/AttributeHelpers/Counter.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers.pm line 23 MooseX::AttributeHelpers::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/AttributeHelpers.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute/Role/Meta/Class.pm line 6 MooseX::ClassAttribute::Role::Meta::Class::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/ClassAttribute/Role/Meta/Class.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute.pm line 11 MooseX::ClassAttribute::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/ClassAttribute.pm called at /usr/lib/perl5/site_perl/5.8.8/Olson/Abbreviations.pm line 6 Olson::Abbreviations::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require Olson/Abbreviations.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTime/ButMaintained.pm line 10 MooseX::Types::DateTime::ButMaintained::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/Types/DateTime/ButMaintained.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTimeX.pm line 9 MooseX::Types::DateTimeX::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require MooseX/Types/DateTimeX.pm called at /usr/lib/perl5/site_perl/5.8.8/Net/Amazon/S3/Client/Bucket.pm line 5 Net::Amazon::S3::Client::Bucket::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require Net/Amazon/S3/Client/Bucket.pm called at /usr/lib/perl5/site_perl/5.8.8/Net/Amazon/S3.pm line 111 Net::Amazon::S3::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require Net/Amazon/S3.pm called at /home/atrails/www/cgi-bin/main.pm line 1633 main::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 require main.pm called at /home/atrails/cron/meetup.pl line 20 main::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Counter.pm line 0 Attribute (+type_constraint) of class MooseX::AttributeHelpers::Number has no associated methods (did you mean to provide an "is" argument?) at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Attribute.pm line 551 Moose::Meta::Attribute::_check_associated_methods('Moose::Meta::Attribute=HASH(0xa4ea48c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Class.pm line 303 Moose::Meta::Class::add_attribute('Moose::Meta::Class=HASH(0xa4f778c)', 'Moose::Meta::Attribute=HASH(0xa4ea48c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 142 Moose::Meta::Role::Application::ToClass::apply_attributes('Moose::Meta::Role::Application::ToClass=HASH(0xa4f8014)', 'Moose::Meta::Role=HASH(0xa38b764)', 'Moose::Meta::Class=HASH(0xa4f778c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application.pm line 72 Moose::Meta::Role::Application::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa4f8014)', 'Moose::Meta::Role=HASH(0xa38b764)', 'Moose::Meta::Class=HASH(0xa4f778c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 31 Moose::Meta::Role::Application::ToClass::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa4f8014)', 'Moose::Meta::Role=HASH(0xa38b764)', 'Moose::Meta::Class=HASH(0xa4f778c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role.pm line 419 Moose::Meta::Role::apply('Moose::Meta::Role=HASH(0xa38b764)', 'Moose::Meta::Class=HASH(0xa4f778c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 132 Moose::Util::_apply_all_roles('Moose::Meta::Class=HASH(0xa4f778c)', 'undef', 'MooseX::AttributeHelpers::Trait::Number') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 86 Moose::Util::apply_all_roles('Moose::Meta::Class=HASH(0xa4f778c)', 'MooseX::AttributeHelpers::Trait::Number') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose.pm line 57 Moose::with('Moose::Meta::Class=HASH(0xa4f778c)', 'MooseX::AttributeHelpers::Trait::Number') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Exporter.pm line 293 Moose::with('MooseX::AttributeHelpers::Trait::Number') called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 9 require MooseX/AttributeHelpers/Number.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers.pm line 24 MooseX::AttributeHelpers::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/AttributeHelpers.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute/Role/Meta/Class.pm line 6 MooseX::ClassAttribute::Role::Meta::Class::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/ClassAttribute/Role/Meta/Class.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute.pm line 11 MooseX::ClassAttribute::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/ClassAttribute.pm called at /usr/lib/perl5/site_perl/5.8.8/Olson/Abbreviations.pm line 6 Olson::Abbreviations::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require Olson/Abbreviations.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTime/ButMaintained.pm line 10 MooseX::Types::DateTime::ButMaintained::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/Types/DateTime/ButMaintained.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTimeX.pm line 9 MooseX::Types::DateTimeX::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/Types/DateTimeX.pm called at /usr/lib/perl5/site_perl/5.8.8/Net/Amazon/S3/Client/Bucket.pm line 5 Net::Amazon::S3::Client::Bucket::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require Net/Amazon/S3/Client/Bucket.pm called at /usr/lib/perl5/site_perl/5.8.8/Net/Amazon/S3.pm line 111 Net::Amazon::S3::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require Net/Amazon/S3.pm called at /home/atrails/www/cgi-bin/main.pm line 1633 main::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require main.pm called at /home/atrails/cron/meetup.pl line 20 main::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 Attribute (+default) of class MooseX::AttributeHelpers::Number has no associated methods (did you mean to provide an "is" argument?) at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Attribute.pm line 551 Moose::Meta::Attribute::_check_associated_methods('Moose::Meta::Attribute=HASH(0xa4f7804)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Class.pm line 303 Moose::Meta::Class::add_attribute('Moose::Meta::Class=HASH(0xa4f778c)', 'Moose::Meta::Attribute=HASH(0xa4f7804)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 142 Moose::Meta::Role::Application::ToClass::apply_attributes('Moose::Meta::Role::Application::ToClass=HASH(0xa4f8014)', 'Moose::Meta::Role=HASH(0xa38b764)', 'Moose::Meta::Class=HASH(0xa4f778c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application.pm line 72 Moose::Meta::Role::Application::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa4f8014)', 'Moose::Meta::Role=HASH(0xa38b764)', 'Moose::Meta::Class=HASH(0xa4f778c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 31 Moose::Meta::Role::Application::ToClass::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa4f8014)', 'Moose::Meta::Role=HASH(0xa38b764)', 'Moose::Meta::Class=HASH(0xa4f778c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role.pm line 419 Moose::Meta::Role::apply('Moose::Meta::Role=HASH(0xa38b764)', 'Moose::Meta::Class=HASH(0xa4f778c)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 132 Moose::Util::_apply_all_roles('Moose::Meta::Class=HASH(0xa4f778c)', 'undef', 'MooseX::AttributeHelpers::Trait::Number') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 86 Moose::Util::apply_all_roles('Moose::Meta::Class=HASH(0xa4f778c)', 'MooseX::AttributeHelpers::Trait::Number') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose.pm line 57 Moose::with('Moose::Meta::Class=HASH(0xa4f778c)', 'MooseX::AttributeHelpers::Trait::Number') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Exporter.pm line 293 Moose::with('MooseX::AttributeHelpers::Trait::Number') called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 9 require MooseX/AttributeHelpers/Number.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers.pm line 24 MooseX::AttributeHelpers::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/AttributeHelpers.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute/Role/Meta/Class.pm line 6 MooseX::ClassAttribute::Role::Meta::Class::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/ClassAttribute/Role/Meta/Class.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute.pm line 11 MooseX::ClassAttribute::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/ClassAttribute.pm called at /usr/lib/perl5/site_perl/5.8.8/Olson/Abbreviations.pm line 6 Olson::Abbreviations::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require Olson/Abbreviations.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTime/ButMaintained.pm line 10 MooseX::Types::DateTime::ButMaintained::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/Types/DateTime/ButMaintained.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTimeX.pm line 9 MooseX::Types::DateTimeX::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require MooseX/Types/DateTimeX.pm called at /usr/lib/perl5/site_perl/5.8.8/Net/Amazon/S3/Client/Bucket.pm line 5 Net::Amazon::S3::Client::Bucket::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require Net/Amazon/S3/Client/Bucket.pm called at /usr/lib/perl5/site_perl/5.8.8/Net/Amazon/S3.pm line 111 Net::Amazon::S3::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require Net/Amazon/S3.pm called at /home/atrails/www/cgi-bin/main.pm line 1633 main::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 require main.pm called at /home/atrails/cron/meetup.pl line 20 main::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/Number.pm line 0 Attribute (+type_constraint) of class MooseX::AttributeHelpers::String has no associated methods (did you mean to provide an "is" argument?) at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Attribute.pm line 551 Moose::Meta::Attribute::_check_associated_methods('Moose::Meta::Attribute=HASH(0xa4fdae0)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Class.pm line 303 Moose::Meta::Class::add_attribute('Moose::Meta::Class=HASH(0xa4fd5c4)', 'Moose::Meta::Attribute=HASH(0xa4fdae0)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 142 Moose::Meta::Role::Application::ToClass::apply_attributes('Moose::Meta::Role::Application::ToClass=HASH(0xa5002d8)', 'Moose::Meta::Role=HASH(0xa42a690)', 'Moose::Meta::Class=HASH(0xa4fd5c4)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application.pm line 72 Moose::Meta::Role::Application::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa5002d8)', 'Moose::Meta::Role=HASH(0xa42a690)', 'Moose::Meta::Class=HASH(0xa4fd5c4)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role/Application/ToClass.pm line 31 Moose::Meta::Role::Application::ToClass::apply('Moose::Meta::Role::Application::ToClass=HASH(0xa5002d8)', 'Moose::Meta::Role=HASH(0xa42a690)', 'Moose::Meta::Class=HASH(0xa4fd5c4)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Meta/Role.pm line 419 Moose::Meta::Role::apply('Moose::Meta::Role=HASH(0xa42a690)', 'Moose::Meta::Class=HASH(0xa4fd5c4)') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 132 Moose::Util::_apply_all_roles('Moose::Meta::Class=HASH(0xa4fd5c4)', 'undef', 'MooseX::AttributeHelpers::Trait::String') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Util.pm line 86 Moose::Util::apply_all_roles('Moose::Meta::Class=HASH(0xa4fd5c4)', 'MooseX::AttributeHelpers::Trait::String') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose.pm line 57 Moose::with('Moose::Meta::Class=HASH(0xa4fd5c4)', 'MooseX::AttributeHelpers::Trait::String') called at /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/Moose/Exporter.pm line 293 Moose::with('MooseX::AttributeHelpers::Trait::String') called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 10 require MooseX/AttributeHelpers/String.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers.pm line 25 MooseX::AttributeHelpers::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 require MooseX/AttributeHelpers.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute/Role/Meta/Class.pm line 6 MooseX::ClassAttribute::Role::Meta::Class::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 require MooseX/ClassAttribute/Role/Meta/Class.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/ClassAttribute.pm line 11 MooseX::ClassAttribute::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 require MooseX/ClassAttribute.pm called at /usr/lib/perl5/site_perl/5.8.8/Olson/Abbreviations.pm line 6 Olson::Abbreviations::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 require Olson/Abbreviations.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTime/ButMaintained.pm line 10 MooseX::Types::DateTime::ButMaintained::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 require MooseX/Types/DateTime/ButMaintained.pm called at /usr/lib/perl5/site_perl/5.8.8/MooseX/Types/DateTimeX.pm line 9 MooseX::Types::DateTimeX::BEGIN() called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 eval {...} called at /usr/lib/perl5/site_perl/5.8.8/MooseX/AttributeHelpers/String.pm line 0 require MooseX/Types/DateTimeX.pm called at /usr/lib/perl5/site_perl/5.8.8/Net/Amazon/S3/Client/Bucket.pm line 5 Net::Amazon::S3::Client::Bucket::BEGIN() called at /usr/lib/perl5/site_per

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  • Compiler error when using abstract types

    - by Dylan
    I'm trying to implement a "protocol helper" trait that is responsible for matching up Prompts and Responses. The eventual goal is to have an object that defines the various Prompt and Response classes as subclasses of a sealed trait, then have a class that mixes in the ProtocolSupport trait for that Protocol object. The problem is that my current approach won't compile, even though I'm fairly sure it should. Here's a distilled version of what I've got: trait Protocol { type Response type Prompt <: BasePrompt trait BasePrompt { type Data def validate(response: Response): Validated[Data] } } trait ProtocolSupport[P <: Protocol] { def foo(prompt: P#Prompt, response: P#Response) = { // compiler error prompt.validate(response) } } The compiler doesn't like the response as an argument to prompt.validate: [error] found : response.type (with underlying type P#Response) [error] required: _4.Response where val _4: P [error] prompt.validate(response) [error] ^ This isn't very helpful.. it seems to say that it wants a P.Response but that's exactly what I'm giving it, so what's the problem?

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  • Why people define class, trait, object inside another object in Scala?

    - by Zwcat
    Ok, I'll explain why I ask this question. I begin to read Lift 2.2 source code these days. In Lift, I found that, define inner class and inner trait are very heavily used. object Menu has 2 inner traits and 4 inner classes. object Loc has 18 inner classes, 5 inner traits, 7 inner objects. There're tons of codes write like this. I wanna to know why the author write it like this. Is it because it's the author's personal taste or a powerful use of language feature?

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  • Usage of @specialized in traits

    - by paradigmatic
    I have a trait and an implementation looking like: trait Foo[A] { def bar[B >: A: Ordering]: Foo[B] } class FooImpl[A]( val a: A, val values: List[Foo[A]] ) extends Foo[A] { def bar[B >: A] = { /* concrete implementation */} } I would like to use the @specialized annotation on A and B to avoid autoboxing. Do I need to use it in both trait and implementation, only in implementation, or only in trait ?

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  • Why does Option not extend the Iterable trait directly?

    - by oxbow_lakes
    Option is implicitly convertible to an Iterable - but why does it not just just implement Iterable directly: def iterator = new Iterator[A] { var end = !isDefined def next() = { val n = if (end) throw new NoSuchElementException() else get end = true n } def hasNext = !end } EDIT: In fact it's even weider than that because in 2.8 Option does declare an iterator method: def iterator: Iterator[A] = if (isEmpty) Iterator.empty else Iterator.single(this.get)

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  • How can I write a function template for all types with a particular type trait?

    - by TC
    Consider the following example: struct Scanner { template <typename T> T get(); }; template <> string Scanner::get() { return string("string"); } template <> int Scanner::get() { return 10; } int main() { Scanner scanner; string s = scanner.get<string>(); int i = scanner.get<int>(); } The Scanner class is used to extract tokens from some source. The above code works fine, but fails when I try to get other integral types like a char or an unsigned int. The code to read these types is exactly the same as the code to read an int. I could just duplicate the code for all other integral types I'd like to read, but I'd rather define one function template for all integral types. I've tried the following: struct Scanner { template <typename T> typename enable_if<boost::is_integral<T>, T>::type get(); }; Which works like a charm, but I am unsure how to get Scanner::get<string>() to function again. So, how can I write code so that I can do scanner.get<string>() and scanner.get<any integral type>() and have a single definition to read all integral types? Update: bonus question: What if I want to accept more than one range of classes based on some traits? For example: how should I approach this problem if I want to have three get functions that accept (i) integral types (ii) floating point types (iii) strings, respectively.

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  • Scala factory pattern returns unusable abstract type

    - by GGGforce
    Please let me know how to make the following bit of code work as intended. The problem is that the Scala compiler doesn't understand that my factory is returning a concrete class, so my object can't be used later. Can TypeTags or type parameters help? Or do I need to refactor the code some other way? I'm (obviously) new to Scala. trait Animal trait DomesticatedAnimal extends Animal trait Pet extends DomesticatedAnimal {var name: String = _} class Wolf extends Animal class Cow extends DomesticatedAnimal class Dog extends Pet object Animal { def apply(aType: String) = { aType match { case "wolf" => new Wolf case "cow" => new Cow case "dog" => new Dog } } } def name(a: Pet, name: String) { a.name = name println(a +"'s name is: " + a.name) } val d = Animal("dog") name(d, "fred") The last line of code fails because the compiler thinks d is an Animal, not a Dog.

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  • cannot override a concrete member without a third member that's overridden by both

    - by huynhjl
    What does the following error message mean? cannot override a concrete member without a third member that's overridden by both (this rule is designed to prevent ``accidental overrides''); I was trying to do stackable trait modifications. It's a little bit after the fact since I already have a hierarchy in place and I'm trying to modify the behavior without having to rewrite a lot of code. I have a base class called AbstractProcessor that defines an abstract method sort of like this: class AbstractProcessor { def onPush(i:Info): Unit } I have a couple existing traits, to implement different onPush behaviors. trait Pass1 { def onPush(i:Info): Unit = { ... } } trait Pass2 { def onPush(i:Info): Unit = { ... } } So that allows me to use new AbstractProcessor with Pass1 or new AbstractProcessor with Pass2. Now I would like to do some processing before and after the onPush call in Pass1 and Pass2 while minimizing code changes to AbstractProcessor and Pass1 and Pass2. I thought of creating a trait that does something like this: trait Custom extends AbstractProcessor { abstract override def onPush(i:Info): Unit = { // do stuff before super.onPush(i) // do stuff after } And using it with new AbstractProcessor with Pass1 with Custom and I got that error message.

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