lyng/docs/Iterable.md

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# Iterable interface
The interface for anything that can be iterated, e.g. finite or infinite ordered set of data that can be accessed sequentially. Almost any data container in `Lyng` implements it: `List`, `Set`, `Buffer`, `RingBuffer`, `BitBuffer`, `Range` and many others are `Iterable`, also `Collection` and `Array` interfaces inherit it.
`Map` and `String` have `Iterable` members to access its contents too.
## Definition:
Iterable is a class that provides function that creates _the iterator_:
class Iterable {
abstract fun iterator()
}
Note that each call of `iterator()` must provide an independent iterator.
Iterator itself is a simple interface that should provide only to method:
class Iterator {
abstract fun hasNext(): Bool
fun next(): Obj
}
Just remember at this stage typed declarations are not yet supported.
Having `Iterable` in base classes allows to use it in for loop. Also, each `Iterable` has some utility functions available, for example
val r = 1..10 // Range is Iterable!
assertEquals( [9,10], r.takeLast(2).toList() )
assertEquals( [1,2,3], r.take(3).toList() )
assertEquals( [9,10], r.drop(8).toList() )
assertEquals( [1,2], r.dropLast(8).toList() )
>>> void
## joinToString
This methods convert any iterable to a string joining string representation of each element, optionally transforming it and joining using specified suffix.
Iterable.joinToString(suffux=' ', transform=null)
- if `Iterable` `isEmpty`, the empty string `""` is returned.
- `suffix` is inserted between items when there are more than one.
- `transform` of specified is applied to each element, otherwise its `toString()` method is used.
Here is the sample:
assertEquals( (1..3).joinToString(), "1 2 3")
assertEquals( (1..3).joinToString(":"), "1:2:3")
assertEquals( (1..3).joinToString { it * 10 }, "10 20 30")
>>> void
## Instance methods:
| fun/method | description |
|-------------------|---------------------------------------------------------------------------|
| toList() | create a list from iterable |
| toSet() | create a set from iterable |
| contains(i) | check that iterable contains `i` |
| `i in iterator` | same as `contains(i)` |
| isEmpty() | check iterable is empty |
| forEach(f) | call f for each element |
| toMap() | create a map from list of key-value pairs (arrays of 2 items or like) |
| map(f) | create a list of values returned by `f` called for each element of the iterable |
| indexOf(i) | return index if the first encounter of i or a negative value if not found |
| associateBy(kf) | create a map where keys are returned by kf that will be called for each element |
| first | first element (1) |
| last | last element (1) |
| take(n) | return [Iterable] of up to n first elements |
| taleLast(n) | return [Iterable] of up to n last elements |
| drop(n) | return new [Iterable] without first n elements |
| dropLast(n) | return new [Iterable] without last n elements |
| joinToString(s,t) | convert iterable to string, see (2) |
(1)
: throws `NoSuchElementException` if there is no such element
(2)
: `joinToString(suffix=" ",transform=null)`: suffix is inserted between items if there are more than one, trasnfom is optional function applied to each item that must return result string for an item, otherwise `item.toString()` is used.
fun Iterable.toList(): List
fun Iterable.toSet(): Set
fun Iterable.indexOf(element): Int
fun Iterable.contains(element): Bool
fun Iterable.isEmpty(element): Bool
fun Iterable.forEach(block: (Any?)->Void ): Void
fun Iterable.map(block: (Any?)->Void ): List
fun Iterable.associateBy( keyMaker: (Any?)->Any): Map
## Abstract methods:
fun iterator(): Iterator
Creates a list by iterating to the end. So, the Iterator should be finite to be used with it.
## Included in interfaces:
- [Collection], Array, [List]
## Implemented in classes:
- [List], [Range], [Buffer](Buffer.md), [BitBuffer], [Buffer], [Set], [RingBuffer]
[List]: List.md
[Range]: Range.md
[Set]: Set.md
[RingBuffer]: RingBuffer.md