NDArrayCollector

A collector to store NDArrays. It provides a scope, NDArrays allocated in the scope can either

• be disposed automatically when the code block finishes, or
  
• simply be collected for future usage.
  If the return type of scope is NDArray or NDArrayFuncReturn, the collector is smart enough NOT to collect or dispose the returned NDArray.
  However in other cases, it is users' responsibility NOT to leak allocated NDArrays outside, (e.g., store to a global variable and use later, pass to another thread, etc.)
  Usage Example:

   val a = NDArray.array(Array(-1f, 0f, 1f, 2f, 3f, 4f), shape = Shape(2, 3))
   val res = NDArrayCollector.auto().withScope {
     (NDArray.relu(a) + a).toArray
   }
  

  In the case above, the intermediate NDArrays (created by NDArray.relu and +) will be disposed automatically.
  User can also decide to dispose the collected NDArrays later:
  

   val collector = NDArrayCollector.manual()
   val res = collector.withScope {
     (NDArray.relu(a) + a).toArray
   }
   collector.foreach(_.dispose())
  

  For Java users:
  

   NDArray a = NDArray.array(new float[]{-1f, 0f, 1f, 2f, 3f, 4f},
                             Shape.create(2, 3), Context.cpu(0));
   float[] sliced = NDArrayCollector.auto().withScope(
     new scala.runtime.AbstractFunction0() {
     @Override
     public float[] apply() {
       a.slice(0, 1).toArray();
     }
   });