Packages > pkl > pkl.base

Listing0.27.0

Overview
Properties
Methods

class Listing<out Element> extends Object

An object containing an ordered sequence of elements.

Known subtypes:
Known usages:
All versions:

Properties

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hidden

default: (Int) -> Element

The function used to compute the default value for a listing element given its index.
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length: Int

The number of elements in this listing.
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isEmpty: Boolean

Tells if this listing is empty, that is, has zero elements.
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lastIndex: Int

The index of the last element in this listing (same as length - 1).

Returns -1 for an empty list.
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isDistinct: Boolean

Tells if this listing has no duplicate elements.

Also known as:

isUnique
Facts:
```
new Listing { 1; 2; 3 }.isDistinct
!new Listing { 1; 2; 1 }.isDistinct
```
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distinct: Listing<Element>

Removes duplicate elements from this listing, preserving the first occurrence.

Also known as:

unique
Facts:
```
new Listing { 1; 2; 3 }.distinct == new Listing { 1; 2; 3 }
new Listing { 1; 2; 1 }.distinct == new Listing { 1; 2 }
```
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first: Element

The first element in this listing.
Throws if this listing is empty.

Facts:
```
new Listing { 1 ; 2 ; 3 }.first == 1
import("pkl:test").catch(() -> new Listing {}.first)
```
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firstOrNull: Element?

Same as first but returns null if this listing is empty.
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last: Element

The last element in this listing.
Throws if this listing is empty.

Facts:
```
new Listing { 1 ; 2 ; 3 }.last == 3
import("pkl:test").catch(() -> new Listing {}.last)
```
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lastOrNull: Element?

Same as last but returns null if this listing is empty.

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single: Element

The single element in this listing.

Throws if this listing does not have exactly one element.

Facts:

new Listing { 1 }.single == 1
import("pkl:test").catch(() -> new Listing {}.single)
import("pkl:test").catch(() -> new Listing { 1 ; 2 ; 3 }.single)

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singleOrNull: Element?

Same as single but returns null if this collection is empty or has more than one element.

Methods(show inherited)

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function

Any.getClass(): Class (pkl.base)

Returns the class of this.
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function

Any.toString(): String (pkl.base)

Returns a string representation of this.

This method is used to convert the values of string interpolation expressions to strings.
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function

Any.ifNonNull<Result>(transform: (NonNull) -> Result): Result? (pkl.base)

Returns this |> transform if this is non-null, and null otherwise.

This method is the complement of the ?? operator and the equivalent of an Option type's map and flatMap methods.

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function

getOrNull(index: Int): Element?

Returns the element at index.

Returns null if index is outside the bounds of this listing.

Facts:

new Listing { 3 ; 9 ; 6 }.getOrNull(0) == 3
new Listing { 3 ; 9 ; 6 }.getOrNull(1) == 9
new Listing { 3 ; 9 ; 6 }.getOrNull(2) == 6
new Listing { 3 ; 9 ; 6 }.getOrNull(-1) == null
new Listing { 3 ; 9 ; 6 }.getOrNull(3) == null
new Listing { 3 ; 9 ; 6 }.getOrNull(99) == null

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function
isDistinctBy(selector: (Element) -> Any): Boolean

Tells if this listing has no elements that are duplicates after applying selector.

Also known as:

isUniqueBy
Facts:
```
new Listing { "a"; "ab"; "abc" }.isDistinctBy((it) -> it.length)
!new Listing { "a"; "ab"; "c" }.isDistinctBy((it) -> it.length)
```
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function
distinctBy(selector: (Element) -> Any): Listing<Element>

Removes elements that are duplicates after applying selector from this listing, preserving the first occurrence.

Also known as:

uniqueBy
Facts:
```
new Listing { "a"; "ab"; "abc" }.distinctBy((it) -> it.length) == new Listing { "a"; "ab"; "abc" }
new Listing { "a"; "ab"; "c" }.distinctBy((it) -> it.length) == new Listing { "a"; "ab" }
```
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function

every(predicate: (Element) -> Boolean): Boolean

Tells if predicate holds for every element of this listing.

Returns true for an empty listing.
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function

any(predicate: (Element) -> Boolean): Boolean

Tells if predicate holds for at least one element of this listing.

Returns false for an empty listing.

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function

contains(element: Element): Boolean

Tests if element is contained in this listing.

Facts:

new Listing { 1 ; 2 ; 3 }.contains(1)
new Listing { 1 ; 2 ; 3 }.contains(2)
new Listing { 1 ; 2 ; 3 }.contains(3)
!new Listing { 1 ; 2 ; 3 }.contains(4)

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function

fold<Result>(initial: Result, operator: (Result, Element) -> Result): Result

Folds this listing in iteration order using operator, starting with initial.
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function

foldIndexed<Result>(initial: Result, operator: (Int, Result, Element) -> Result): Result

Folds this listing in iteration order using operator, starting with initial.

The first parameter of operator is the zero-based index of the current element.
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function

join(separator: String): String

Converts the elements of this listing to strings and concatenates them inserting separator between elements.
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function

toList(): List<Element>

Converts this listing to a List.
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function

toSet(): Set<Element>

Converts this listing to a Set.