Yes they can, a `trait` that extends a `class` puts a restriction on what `classes` can extend that `trait` - namely, all `classes` that mix-in that `trait` must extend that `class`.

    scala&gt; class Foo
    defined class Foo
    
    scala&gt; trait FooTrait extends Foo
    defined trait FooTrait
    
    scala&gt; val good = new Foo with FooTrait
    good: Foo with FooTrait = $anon$1@773d3f62
    
    scala&gt; class Bar
    defined class Bar
    
    scala&gt; val bad = new Bar with FooTrait
    &lt;console&gt;:10: error: illegal inheritance; superclass Bar
     is not a subclass of the superclass Foo
     of the mixin trait FooTrait
           val bad = new Bar with FooTrait
                                  ^

Can someone please explain to me why the output from the following code is saying that arrays are **not equal**?

    int main()
    {
    
    	int iar1[] = {1,2,3,4,5};
    	int iar2[] = {1,2,3,4,5};
    	
    	if (iar1 == iar2)
    		cout &lt;&lt; &quot;Arrays are equal.&quot;;
    	else
    		cout &lt;&lt; &quot;Arrays are not equal.&quot;;
    
    	return 0;	
    }

Comparing arrays for equality in C++

Is it possible to access post or get parameters via the HttpActionContext object? 

I have a set of sensors that loggs data to a web server that provides a REST api. I would like to introduce some sort of authentication/authorization by letting the sensors include their hardware id in the data and then make a lookup in a database to see if the id exists or not. Since the API provides many web api action methods I would ideally like to use a custom authorization attribute

    public class ApiAuthorizationFilter : AuthorizeAttribute
    {
        protected override bool IsAuthorized(HttpActionContext actionContext)
        {
            return false;
        }
    }
How can I access the post/get data from the actionContext?

EDIT:
Example of POST

    POST /Api/api/ActionMethod/ HTTP/1.1\r\n
    Content-Type: application/json\r\n
    Host: localhost\r\n
    Accept: */*\r\n
    Content-Length:52\r\n
    \r\n
    {&quot;Id&quot;: &#39;121a222bc&#39;, &quot;Time&quot;: &#39;2012-02-02 12:00:00&#39;}\r\n

Have a nice day!



Accessing post or get parameters in custom authorization MVC4 Web Api

I see that traits in Scala are similar to interfaces in Java (but interfaces in Java extend other interfaces, they don&#39;t extend a class). I saw [an example on SO about traits usage][1] where a trait extends a class.

What is the purpose of this? Why can traits extend classes?


  [1]: https://stackoverflow.com/questions/1229743/scala-traits-usage

Why can a Scala trait extend a class?

<p>I see that traits in Scala are similar to interfaces in Java (but interfaces in Java extend other interfaces, they don't extend a class). I saw <a href="https://stackoverflow.com/questions/1229743/scala-traits-usage" target="_blank" rel="noopener noreferrer">an example on SO about traits usage</a> where a trait extends a class.</p>
<p>What is the purpose of this? Why can traits extend classes?</p>


I&#39;m following the Scala course on Coursera.
I&#39;ve started to read the Scala book of Odersky as well.


What I often hear is that it&#39;s not a good idea to throw exceptions in functional languages, because it breaks the control flow and we usually return an Either with the Failure or Success.
It seems also that Scala 2.10 will provide the Try which goes in that direction.

But in the book and the course, Martin Odersky doesn&#39;t seem to say (at least for now) that exceptions are bad, and he uses them a lot.
I also noticed the methods assert / require...

Finally I&#39;m a bit confused because I&#39;d like to follow the best practices but they are not clear and the language seems to go in both directions...

Can someone explain me what i should use in which case?

Throwing exceptions in Scala, what is the &quot;official rule&quot;

What&#39;s the best way to terminate a fold early? As a simplified example, imagine I want to sum up the numbers in an `Iterable`, but if I encounter something I&#39;m not expecting (say an odd number) I might want to terminate. This is a first approximation

    def sumEvenNumbers(nums: Iterable[Int]): Option[Int] = {
      nums.foldLeft (Some(0): Option[Int]) {
        case (Some(s), n) if n % 2 == 0 =&gt; Some(s + n)
        case _ =&gt; None
      }
    }

However, this solution is pretty ugly (as in, if I did a .foreach and a return -- it&#39;d be much cleaner and clearer) and worst of all, it traverses the entire iterable even if it encounters a non-even number.

So what would be the best way to write a fold like this, that terminates early? Should I just go and write this recursively, or is there a more accepted way?



Abort early in a fold

There are path dependent types and I think it is possible to express almost all the features of such languages as Epigram or Agda in Scala, but I&#39;m wondering why Scala does not support [this](http://en.wikipedia.org/wiki/Dependent_type) more explicitly like it does very nicely in other areas (say, DSLs) ?
Anything I&#39;m missing like &quot;it is not necessary&quot; ?

Any reason why scala does not explicitly support dependent types?

I&#39;ve searched for a half-hour, and still cannot figure it out.

In [SIP: Modularizing Language Features][1] there are a number of features which will require explicit &quot;enabling&quot; in Scala 2.10 (`import language.feature`).
Amongst them there is `postfixOps`, to which I just cannot find a reference anywhere. What exactly does this feature allow?

  [1]: http://docs.scala-lang.org/sips/pending/modularizing-language-features.html

Scala&#39;s &quot;postfix ops&quot;

Let&#39;s say I&#39;m getting a (potentially big) list of images to download from some URLs. I&#39;m using Scala, so what I would do is :

    import scala.actors.Futures._
    
    // Retrieve URLs from somewhere
    val urls: List[String] = ...
    
    // Download image (blocking operation)
    val fimages: List[Future[...]] = urls.map (url =&gt; future { download url })
    
    // Do something (display) when complete
    fimages.foreach (_.foreach (display _))

I&#39;m a bit new to Scala, so this still looks a little like magic to me :

  * Is this the right way to do it? Any alternatives if it is not?
  * If I have 100 images to download, will this create 100 threads at once, or will it use a thread pool?
  * Will the last instruction (`display _`) be executed on the main thread, and if not, how can I make sure it is?

Thanks for your advice!

Asynchronous IO in Scala with futures

I&#39;m wondering why PHP Trait (PHP 5.4) cannot implement interfaces.

**Update from user1460043&#39;s answer =&gt; ...cannot require class which uses it to implement a specific interface** 

I understand that it could be obvious, because people could think that if a `Class A` is using a `Trait T` which is implementing an `interface I`, than the `Class A` should be implementing the `interface I` undirectly (and this is not true because `Class A` could rename trait methods).

In my case, my trait is calling methods from the interface that the class using the trait implements. 

The trait is in fact an implementation of some methods of the interface.
So, i want to &quot;design&quot; in the code that every class that want to use my trait have to implement the interface. That would allow the Trait to use class methods defined by the interface and be sure they are existing in the class.

Why PHP Trait can&#39;t implement interfaces?

I was going through the [effective scala slides][1] and it mentions on slide 10 to never use `val` in a `trait` for abstract members and use `def` instead. The slide does not mention in detail why using abstract `val` in a `trait` is an anti-pattern. I would appreciate it if someone can explain best practice around using val vs def in a trait for abstract methods  


  [1]: http://www.slideshare.net/mircodotta/effective-scala

When to use val or def in Scala traits?

Would someone explain when I would want to use [Groovy Traits][1] vs. Mixins (@Mixin) vs. Delegates (@Delegate)? Maybe some trade-offs and design concerns would help.

They all seem to allow for reusing multiple &quot;classes&quot; of behavior. Thanks. :-)

This SO thread was helpful too: https://stackoverflow.com/questions/8527500/difference-between-delegate-and-mixin-ast-transformations-in-groovy

  [1]: http://beta.groovy-lang.org/docs/groovy-2.3.0-SNAPSHOT/html/documentation/core-traits.html

Difference between @Delegate, @Mixin and Traits in Groovy?

What is the best way to define constants that may be used by a number of classes within a namespace? I&#39;m trying to avoid too much inheritance, so extending base classes is not an ideal solution, and I&#39;m struggling to find a good solution using traits. Is this in any way possible in PHP 5.4 or should a different approach be taken?

I have the following situation:

    trait Base
    {
        // Generic functions
    }

    class A 
    {
        use Base;
    }

    class B 
    {
        use Base;
    }

The problem is that it is not possible to define constants in PHP traits. Ideally, I would want something like the following:

    trait Base
    {
        const SOME_CONST = &#39;someconst&#39;;
        const SOME_OTHER_CONST = &#39;someotherconst&#39;;

        // Generic functions
    }

Then these could be accessed though the class that applies the trait:

    echo A::SOME_CONST;
    echo B::SOME_OTHER_CONST;

But due to the limitations of traits this isn&#39;t possible. Any ideas?


PHP traits - defining generic constants

I wanted to implement the `Shl` trait for `Vec`, the code is below. This would make things like `vec &lt;&lt; 4` possible, which would be nice sugar for `vec.push(4)`.

    use std::ops::Shl;
    
    impl&lt;T&gt; Shl&lt;T&gt; for Vec&lt;T&gt; {
        type Output = Vec&lt;T&gt;;
    
        fn shl(&amp;self, elem: &amp;T) -&gt; Vec&lt;T&gt; {
            self.push(*elem);
            *self
        }
    }
    
    fn main() {
        let v = vec![1, 2, 3];
        v &lt;&lt; 4;
    }

The compilation fails with the following error:

&lt;!-- language: none --&gt;

&gt; cannot provide an extension implementation where both trait and type are not defined in this crate [E0117]

or

&lt;!-- language: none --&gt;

&gt; type parameter `T` must be used as the type parameter for some local type (e.g. `MyStruct&lt;T&gt;`); only traits defined in the current crate can be implemented for a type parameter [E0210]

As I understand it, I&#39;d have to patch the stdlib, more specifically the `collections::vec` crate. Is there another way to change this code to compile successfully?



Content Type	Original Author	Original Content on Stackoverflow
Question	Raj	View Question on Stackoverflow
Solution 1 - Scala	adelbertc	View Answer on Stackoverflow

Why can a Scala trait extend a class?

Scala Problem Overview

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Accessing post or get parameters in custom authorization MVC4 Web Api

Comparing arrays for equality in C++

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