mbeckerle commented on a change in pull request #214: Sequences and Separators
Refactoring and Rewrite
URL: https://github.com/apache/incubator-daffodil/pull/214#discussion_r284796903
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File path: daffodil-core/src/main/scala/org/apache/daffodil/dsom/Term.scala
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@@ -803,4 +877,87 @@ trait Term
}
}
+ /**
+ * A zeroLengthDetector is a runtime device used by the unparser to
+ * determine whether a term could unparse to zero length or not.
+ *
+ * Computed statically, because sometimes we know that it is not possible
+ * for the representation to be zero length (e.g., non-nillable ahd
non-defaultable
+ * int always has to have at least one digit.)
+ *
+ * Used by unparsing algorithms that involve separator suppression for
+ * zero-length data.
Review comment:
Add that the point of this is to avoid the overhead of unparser uncertainty
about a separator being needed or not. If you can examine the value with a
zero-length-detector and it gives you a positive answer one way or the other,
you can avoid a great deal of unparser overhead where it has to suspend whether
to emit a separator. If the ZL detector tells you the representation will be
greater than zero length, you can just emit a separator and move on.
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