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

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
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`.
`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 Detail
  - Selector
```
public Selector()
```
- Method Detail
  - 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.

Class Selector

Constructor Summary

Method Summary

Methods inherited from class swim.structure.Expression

Methods inherited from class swim.structure.Value

Methods inherited from class swim.structure.Item

Methods inherited from class java.lang.Object

Methods inherited from interface java.lang.Iterable

Constructor Detail

Selector

Method Detail

isConstant

then

forSelected

mapSelected

evaluate

andThen

get

get

getAttr

getAttr

getItem

getItem

keys

values

children

descendants

filter

filter

invoke

precedence

debug

debugThen

compareTo

compareTo

identity

literal