Module swim.structure

Package swim.structure.selector

Class FilterSelector

java.lang.Object

swim.structure.Item

swim.structure.Value

swim.structure.Expression

swim.structure.Selector

swim.structure.selector.FilterSelector

All Implemented Interfaces:

Comparable<Item>, Iterable<Item>, Debug, Display, Selectee<Item>

public final class FilterSelector
extends Selector
implements Selectee<Item>

A Selector that, when evaluated, yields each Item in interpreter such that evaluating predicate against this Item would select at least one defined result. This is fundamentally different from returning the result itself; for example,

FilterSelector(predicate=GetSelector(key="a")).evaluate(Record(Slot("a",5))

yields the Record itself, NOT just 5.

To accomplish this, FilterSelector itself implements Selectee<Item>.selected by always returning Extant which, crucially, is never null. forSelected still takes the form "if (condition) then subselect"; here, "condition" is true only if predicate.forSelected(interpreter,this) is not null. Thus, the responsibility to ensure that this.selected is invoked only if predicate would select something in Interpreter is in predicate.forSelected--exactly as it should be.

Constructor Summary

Constructors

Constructor	Description
FilterSelector(Selector predicate, Selector then)

Method Summary

Modifier and Type	Method	Description
Selector	andThen(Selector then)	The means to chain Selectors.
protected int	compareTo(Selector that)
<T> Output<T>	debugThen(Output<T> output)
boolean	equals(Object other)
FilterSelector	filter()	Returns a new FilterSelector with this as the predicate.
protected boolean	filterSelected(Interpreter interpreter)
<T> T	forSelected(Interpreter interpreter, Selectee<T> callback)	Evaluates callback.selected against the Items that match this Selector's selection criteria.
int	hashCode()
Item	mapSelected(Interpreter interpreter, Selectee<Item> transform)
Selector	predicate()
Item	selected(Interpreter interpreter)	Always returns Extant, which, crucially, is never null.
Item	substitute(Interpreter interpreter)
Selector	then()	Returns the Selector that this Selector uses to match sub-selections.
int	typeOrder()	Returns the heterogeneous sort order of this Item.

Methods inherited from class swim.structure.Selector

children, compareTo, debug, descendants, evaluate, filter, get, get, getAttr, getAttr, getItem, getItem, identity, invoke, isConstant, keys, literal, precedence, values

Methods inherited from class swim.structure.Expression

and, and, bitwiseAnd, bitwiseAnd, bitwiseNot, bitwiseOr, bitwiseOr, bitwiseXor, bitwiseXor, conditional, conditional, divide, divide, eq, eq, ge, ge, gt, gt, inverse, le, le, lt, lt, minus, minus, modulo, modulo, ne, ne, negative, not, or, or, plus, plus, positive, times, times

Methods inherited from class swim.structure.Value

absent, alias, body, booleanValue, booleanValue, branch, builder, byteValue, byteValue, charValue, charValue, commit, contains, containsKey, containsKey, containsValue, doubleValue, doubleValue, empty, extant, flattened, floatValue, floatValue, fromObject, getField, getField, getSlot, getSlot, head, header, headers, integerValue, integerValue, intValue, intValue, isAliased, isDefined, isDefinite, isDistinct, isMutable, key, keyEquals, lambda, length, longValue, longValue, numberValue, numberValue, removed, removed, shortValue, shortValue, stringValue, stringValue, tag, tail, target, toValue, unflattened

Methods inherited from class swim.structure.Item

appended, appended, appended, appended, appended, appended, appended, appended, cast, cast, coerce, coerce, concat, display, evaluate, globalScope, iterator, max, min, prepended, prepended, prepended, prepended, prepended, prepended, prepended, prepended, substitute, toString, updated, updated, updated, updated, updated, updated, updated, updated, updated, updated, updated, updated, updated, updated, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedAttr, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot, updatedSlot

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Constructor Details

FilterSelector

public FilterSelector(Selector predicate,
 Selector then)

Method Details

predicate

public Selector predicate()

then

public Selector then()

Description copied from class: Selector

Returns the Selector that this Selector uses to match sub-selections.

Specified by:

then in class Selector

forSelected

public <T> T forSelected(Interpreter interpreter,
 Selectee<T> callback)

Description copied from class: Selector

Evaluates callback.selected against the Items that match this Selector's selection criteria. That is, it pushes such Items to interpreter, then invokes callback against it. To support chained Selectors, this is a recursive procedure that invokes forSelected through this.then wherever it exists (which it always does outside of IdentitySelector); we define "subselection" to be such an invocation.

Specified by:

forSelected in class Selector

Returns:

the result of executing callback from the context of the last Selector in the chain formed by Selector then fields.

mapSelected

public Item mapSelected(Interpreter interpreter,
 Selectee<Item> transform)

Specified by:

mapSelected in class Selector

substitute

public Item substitute(Interpreter interpreter)

Overrides:

substitute in class Item

filterSelected

protected boolean filterSelected(Interpreter interpreter)

selected

public Item selected(Interpreter interpreter)

Always returns Extant, which, crucially, is never null. See FilterSelector for an explanation.

Specified by:

selected in interface Selectee<Item>

andThen

public Selector andThen(Selector then)

Description copied from class: Selector

The means to chain Selectors. By intention, this is NOT a strict functional composition: for two Selectors s1 and s2, s1.andThen(s2) DOES NOT NECESSARILY return a new Selector s3 such that s3.evaluate(args) is equivalent to s2.evaluate(s1.evaluate(args)).

The reason for this is that for Selectors like ChildrenSelector that yield (logical) collections, we wish to invoke the next Selector, say a GetSelector, against every result. Under strict functional rules, ChildrenSelector.andThen(someGetSelector).evaluate(args) would instead return at most one defined value regardless of the number of children.

Specified by:

andThen in class Selector

filter

public FilterSelector filter()

Description copied from class: Selector

Returns a new FilterSelector with this as the predicate.

Overrides:

filter in class Selector

typeOrder

public int typeOrder()

Description copied from class: Item

Returns the heterogeneous sort order of this Item. Used to impose a total order on the set of all items. When comparing two items of different types, the items order according to their typeOrder.

Specified by:

typeOrder in class Item

compareTo

protected int compareTo(Selector that)

Specified by:

compareTo in class Selector

equals

public boolean equals(Object other)

Specified by:

equals in class Item

hashCode

public int hashCode()

Specified by:

hashCode in class Item

debugThen

public <T> Output<T> debugThen(Output<T> output)

Specified by:

debugThen in class Selector