Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>An existing runtime object in the JVM has a certain size on the heap. Adding a trait to it would mean altering its size on the heap, and changing its signature.</p> <p>So the only way to go would be to do some kind of transformation at compile time.</p> <p>Mixin composition in Scala occurs at compile time. What compiler could potentially do is create a wrapper B around an existing object A with the same type that simply forwards all calls to the existing object A, and then mix in a trait T to B. This, however, is not implemented. It is questionable when this would be possible, since the object A could be an instance of a final class, which cannot be extended.</p> <p>In summary, mixin composition is not possible on existing object instances.</p> <p>UPDATED:</p> <p>Related to the smart solution proposed by Googol Shan, and generalizing it to work with any trait, this is as far as I got. The idea is to extract the common mixin functionality in the <code>DynamicMixinCompanion</code> trait. The client should then create a companion object extending <code>DynamicMixinCompanion</code> for each trait he wants to have the dynamic mixin functionality for. This companion object requires defining the anonymous trait object gets created (<code>::</code>).</p> <pre><code>trait DynamicMixinCompanion[TT] { implicit def baseObject[OT](o: Mixin[OT]): OT = o.obj def ::[OT](o: OT): Mixin[OT] with TT class Mixin[OT] protected[DynamicMixinCompanion](val obj: OT) } trait OtherTrait { def traitOperation = println("any trait") } object OtherTrait extends DynamicMixinCompanion[OtherTrait] { def ::[T](o: T) = new Mixin(o) with OtherTrait } object Main { def main(args: Array[String]) { val a = "some string" val m = a :: OtherTrait m.traitOperation println(m.length) } } </code></pre>
    singulars
    1. This table or related slice is empty.
    1. POHow to mix-in a trait to instance?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USaxel22
    1. USaxel22
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COJust as minor remark for clarification: the variable `m` is an instance of `OtherTrait` but _not_ an instance of `String`. (It is the `implicit` that "converts" it back to a string whenever needed, at compile time.) You can see this nicely by adding `println("m is instance of String/OtherTrait: " + m.isInstanceOf[String] + "/" + m.isInstanceOf[OtherTrait])` at the end of the `main` function.
      singulars
      1. PO
      1. USHbf
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload