Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>You can use the <em>dynamic scope pattern</em>. More prosaically this means using a thread local variable (scala's <code>DynamicVariable</code> is done just for that) to store the current nesting level. See my answer to this other question for a partical example of this pattern: <a href="https://stackoverflow.com/questions/7069044/how-to-define-a-function-that-takes-a-function-literal-with-an-implicit-paramet/13252952#13252952">How to define a function that takes a function literal (with an implicit parameter) as an argument?</a></p> <p>This is suitable only if you want to know the nesting level for a very specific method though. If you want a generic mecanism that works for any method then this won't work (as you'd need a distinct variable for each method). In this case the only alternative I can think of is to inspect the stack, but not only is it not very reliable, it is also extremely slow.</p> <p><strong>UPDATE</strong>: actually, there <em>is</em> a way to apply the dynamic scope pattern in a generic way (for any possible method). The important part is to be able to implicitly get a unique id for each method. from there, it is just a matter of using this id as a key to associate a <code>DynamicVariable</code> to the method:</p> <pre><code>import scala.util.DynamicVariable object FunctionNestingHelper { private type FunctionId = Class[_] private def getFunctionId( f: Function1[_,_] ): FunctionId = { f.getClass // That's it! Beware, implementation dependant. } private val currentNestings = new DynamicVariable( Map.empty[FunctionId, Int] ) def withFunctionNesting[T]( body: Int =&gt; T ): T = { val id = getFunctionId( body ) val oldNestings = currentNestings.value val oldNesting = oldNestings.getOrElse( id, 0 ) val newNesting = oldNesting + 1 currentNestings.withValue( oldNestings + ( id -&gt; newNesting) ) { body( newNesting ) } } } </code></pre> <p>Usage:</p> <pre><code>import FunctionNestingHelper._ def decorate(f: =&gt; Unit) = withFunctionNesting { nesting: Int =&gt; println("I am decorated " + nesting + "x") ; f } </code></pre> <p>To get a unique id for the method, I actually get an id for a the closure passed to <code>withFunctionNesting</code> (which you must call in the method where you need to retrieve the current nesting). And that's where I err on the implementation dependant side: the <em>id</em> is just the class of the function instance. This does work as expected as of now (because every unary function literal is implemented as exactly one class implementing <code>Function1</code> so the class acts as a unique id), but the reality is that it might well break (although unlikely) in a future version of scala. So use it at your own risk.</p> <p>Finally, I suggest that you first evaluate seriously if Nikita Volkov's suggestion of going more functional would not be a better solution overall.</p>
    singulars
    1. This table or related slice is empty.
    1. POHow to track nested functions in Scala
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USCommunity
    1. USRégis Jean-Gilles
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POHow to track nested functions in Scala
      singulars
      1. PTQuestion
    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. This table or related slice is empty.
 

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