bsloane1650 commented on a change in pull request #207: Added support for
enumerations and TypeValueCalc
URL: https://github.com/apache/incubator-daffodil/pull/207#discussion_r275565958
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File path: daffodil-lib/src/main/scala/org/apache/daffodil/util/Cursor.scala
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@@ -160,18 +196,24 @@ trait CursorImplMixin[AccessorType <:
Accessor[AccessorType]] { self: Cursor[Acc
val res = priorOpKind match {
case Advance => {
priorOpKind = Inspect
- doAdvance(true)
+ doAdvance(true, true)
}
- case Inspect => true // inspect again does nothing.
+ case InspectPure => {
+ priorOpKind = Inspect
+ doAdvance(true, advanceInput=false)
+ }
+ case Inspect => true // inspect again does nothing.
case Unsuccessful => return false
}
// successful
Assert.invariant(isFilled == true || !res)
res
}
- private def doAdvance(isFilledValue: Boolean) = {
- val res = fill()
+ //inpsectPure implemented in InfosetInputter.scala
+
+ private def doAdvance(isFilledValue: Boolean, advanceInput: Boolean) = {
Review comment:
The issue is that in the InfosetCursor implementation, constructing the
object has side effects. So, in order to use the 1 object lookahead, the side
effects associated with creating an object occur when you use the lookahaed,
instead of when you actually consume the object. This means that there is no
way to inspect any aspect of the next object without triggering the side
effects associated with creating it.
InspectPure provides a limited 1 object look ahead that can be used without
triggering the side effects associated with constructing the full object like
inspect would.
In more practical terms, inspectPure provides only the ElementRuntimeData,
while inspect provides a DINode.
This is actually orthogonal to the difference between more traditional
iterators. We would have the same problem with a next()/hasNext()/peek() style
API, as our implementation of peek() would have the same side effects as
inspect() does now.
The API of Cursor itself is actuall pretty sane. The problem comes when we
make InfosetCursor use Accessor[DINode], as that requires making
inspect()/next() have unexpected side-effects.
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