Mihaela Mihaljevic
5ad3cf10fc
A path that is a single forward-axis step from one context node returns its nodes already in document order with no duplicates, so the document-order sort is redundant. AxisNavigation produces the structural forward axes (child, descendant, descendant-or-self, self, following, following-sibling) in document order, deriving sibling order from the same children array the order key compares, so the two can never disagree. This is the common shape after //x compiles and fuses to a single descendant::x step. The attribute axis (whose order interleaves with namespace declarations), the namespace axis (produced in dictionary order), and every reverse axis (nearest-first) are excluded and still sorted. Measured xpath ~7% faster on the 20k-item generated corpus via a same-state A/B, identical results. XPathSingleStepOrderTests pins document order for each included axis, that the reverse axes still normalize, and that multi-step paths still sort. An adversarial order-correctness review found no query whose order or uniqueness the change breaks.
79 lines
3.1 KiB
Swift
79 lines
3.1 KiB
Swift
extension PureXML.XPath {
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/// The thirteen XPath 1.0 axes. Every axis is reachable now that the tree is
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/// parent-aware, so upward and sibling navigation are first-class.
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enum Axis: Equatable {
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case child
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case descendant
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case parent
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case ancestor
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case followingSibling
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case precedingSibling
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case following
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case preceding
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case attribute
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case namespace
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case selfAxis
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case descendantOrSelf
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case ancestorOrSelf
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/// Whether the axis is a reverse axis (its nodes are numbered in reverse
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/// document order for positional predicates).
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var isReverse: Bool {
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switch self {
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case .parent, .ancestor, .precedingSibling, .preceding, .ancestorOrSelf:
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true
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default:
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false
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}
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}
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/// Whether the axis, taken from a SINGLE context node, yields its nodes
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/// already in document order with no duplicates, so a one-step path over
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/// it needs neither the de-duplication nor the document-order sort. True
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/// for the structural forward axes, which `AxisNavigation` produces in
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/// document order (child by child-array order, descendant by pre-order,
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/// the following families by document position). The attribute axis is
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/// excluded because its order interleaves with namespace declarations,
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/// and the namespace axis because its nodes are produced in dictionary
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/// (hash) order; the sort normalizes both, so they are left to it.
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var preservesDocumentOrderFromSingleContext: Bool {
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switch self {
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case .child, .descendant, .descendantOrSelf, .selfAxis, .followingSibling, .following: true
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default: false
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}
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}
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/// Whether the axis yields disjoint node-sets from distinct context nodes,
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/// so accumulating its results across a step's context nodes can never
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/// produce a duplicate and needs no cross-context de-duplication. A child,
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/// attribute, or namespace node belongs to exactly one element, and the
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/// self axis maps each distinct context to itself; every other axis
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/// (descendant, ancestor, the siblings, following/preceding, parent) can
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/// reach one node from two different contexts.
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var yieldsDisjointResults: Bool {
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switch self {
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case .child, .attribute, .namespace, .selfAxis: true
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default: false
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}
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}
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/// The principal node kind of the axis: attributes for the attribute axis,
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/// namespaces for the namespace axis, elements otherwise. Governs what a
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/// name test or `*` selects.
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var principalKind: PrincipalKind {
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switch self {
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case .attribute: .attribute
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case .namespace: .namespace
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default: .element
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}
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}
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}
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/// The principal node kind selected by name tests on an axis.
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enum PrincipalKind: Equatable {
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case element
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case attribute
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case namespace
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}
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}
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