Module swim.structure

Package swim.structure

Class Selector

java.lang.Object

swim.structure.Item

swim.structure.Value

swim.structure.Expression

swim.structure.Selector

All Implemented Interfaces:

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

Direct Known Subclasses:

ChildrenSelector, DescendantsSelector, FilterSelector, GetAttrSelector, GetItemSelector, GetSelector, IdentitySelector, KeysSelector, LiteralSelector, ValuesSelector

public abstract class Selector
extends Expression

An Expression that returns references to Items when it is evaluated. Because most application-level Items are Records, a way to only extract certain parts of Records is often required. Technically, this can be accomplished without Selectors to some extent because the Record class implements java.util.List<Item> and (implicitly) java.util.Map<Value,Value>; however, Selectors additionally expose functional patterns that enhance composability, providing a foundation on top of which expression languages can be built.

Constructor Summary

Constructors

Constructor	Description
Selector()

Method Summary

Modifier and Type	Method	Description
abstract Selector	andThen(Selector then)	The means to chain Selectors.
Selector	children()	An abstraction over andThen(swim.structure.Selector) where then is the ChildrenSelector.
int	compareTo(Item other)
protected abstract int	compareTo(Selector that)
<T> Output<T>	debug(Output<T> output)	Writes a developer readable, debug-formatted string representation of this object to output.
abstract <T> Output<T>	debugThen(Output<T> output)
Selector	descendants()	An abstraction over andThen(swim.structure.Selector) where then is the DescendantsSelector.
final Item	evaluate(Interpreter interpreter)	Evaluates this Selector against some Interpreter.
FilterSelector	filter()	Returns a new FilterSelector with this as the predicate.
Selector	filter(Item predicate)	An abstraction over andThen(swim.structure.Selector) where then is a FilterSelector.
abstract <T> T	forSelected(Interpreter interpreter, Selectee<T> callback)	Evaluates callback.selected against the Items that match this Selector's selection criteria.
Selector	get(String key)	An abstraction over andThen(swim.structure.Selector) where then is a GetSelector.
Selector	get(Value key)	An abstraction over andThen(swim.structure.Selector) where then is a GetSelector.
Selector	getAttr(String key)	An abstraction over andThen(swim.structure.Selector) where then is a GetAttrSelector.
Selector	getAttr(Text key)	An abstraction over andThen(swim.structure.Selector) where then is a GetAttrSelector.
Selector	getItem(int index)	An abstraction over andThen(swim.structure.Selector) where then is a GetItemSelector.
Selector	getItem(Num index)	An abstraction over andThen(swim.structure.Selector) where then is a GetItemSelector.
static Selector	identity()
Operator	invoke(Value args)	Creates, but does not evaluate, an InvokeOperator where this Selector evaluates to the operator.
boolean	isConstant()	Returns true if this Item always evaluates to the same Item.
Selector	keys()	An abstraction over andThen(swim.structure.Selector) where then is the KeysSelector.
static Selector	literal(Item item)	Lifts item into a LiteralSelector if it is not already a Selector.
abstract Item	mapSelected(Interpreter interpreter, Selectee<Item> transform)
int	precedence()
abstract Selector	then()	Returns the Selector that this Selector uses to match sub-selections.
Selector	values()	An abstraction over andThen(swim.structure.Selector) where then is the ValuesSelector.

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, equals, evaluate, globalScope, hashCode, iterator, max, min, prepended, prepended, prepended, prepended, prepended, prepended, prepended, prepended, substitute, substitute, toString, typeOrder, 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

Selector

public Selector()

Method Details

isConstant

public boolean isConstant()

Description copied from class: Item

Returns true if this Item always evaluates to the same Item.

Specified by:

isConstant in class Item

then

public abstract Selector then()

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

forSelected

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

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.

Returns:

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

mapSelected

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

evaluate

public final Item evaluate(Interpreter interpreter)

Evaluates this Selector against some Interpreter. This is accomplished by creating a new SelecteeBuilder and populating its internal Record with (recursive) calls to forSelected(swim.structure.Interpreter, swim.structure.Selectee<T>).

Overrides:

evaluate in class Item

andThen

public abstract Selector andThen(Selector then)

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.

get

public Selector get(Value key)

An abstraction over andThen(swim.structure.Selector) where then is a GetSelector.

Overrides:

get in class Value

Parameters:

key - the key field in the composing GetSelector.

get

public Selector get(String key)

An abstraction over andThen(swim.structure.Selector) where then is a GetSelector.

Overrides:

get in class Value

Parameters:

key - the key field in the composing GetSelector.

getAttr

public Selector getAttr(Text key)

An abstraction over andThen(swim.structure.Selector) where then is a GetAttrSelector.

Overrides:

getAttr in class Value

Parameters:

key - the key field in the composing GetAttrSelector.

getAttr

public Selector getAttr(String key)

An abstraction over andThen(swim.structure.Selector) where then is a GetAttrSelector.

Overrides:

getAttr in class Value

Parameters:

key - the key field in the composing GetAttrSelector.

getItem

public Selector getItem(Num index)

An abstraction over andThen(swim.structure.Selector) where then is a GetItemSelector.

Parameters:

index - the index field in the composing GetItemSelector.

getItem

public Selector getItem(int index)

An abstraction over andThen(swim.structure.Selector) where then is a GetItemSelector.

Overrides:

getItem in class Value

Parameters:

index - the index field in the composing GetItemSelector.

keys

public Selector keys()

An abstraction over andThen(swim.structure.Selector) where then is the KeysSelector.

values

public Selector values()

An abstraction over andThen(swim.structure.Selector) where then is the ValuesSelector.

children

public Selector children()

An abstraction over andThen(swim.structure.Selector) where then is the ChildrenSelector.

descendants

public Selector descendants()

An abstraction over andThen(swim.structure.Selector) where then is the DescendantsSelector.

filter

public FilterSelector filter()

Returns a new FilterSelector with this as the predicate.

Overrides:

filter in class Item

filter

public Selector filter(Item predicate)

An abstraction over andThen(swim.structure.Selector) where then is a FilterSelector.

Overrides:

filter in class Item

invoke

public Operator invoke(Value args)

Creates, but does not evaluate, an InvokeOperator where this Selector evaluates to the operator.

Overrides:

invoke in class Item

precedence

public int precedence()

Overrides:

precedence in class Item

debug

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

Description copied from interface: Debug

Writes a developer readable, debug-formatted string representation of this object to output.

Specified by:

debug in interface Debug

Specified by:

debug in class Item

Returns:

the continuation of the output.

debugThen

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

compareTo

public int compareTo(Item other)

Specified by:

compareTo in interface Comparable<Item>

Specified by:

compareTo in class Item

compareTo

protected abstract int compareTo(Selector that)

identity

public static Selector identity()

literal

public static Selector literal(Item item)

Lifts item into a LiteralSelector if it is not already a Selector.