Iterable

Iteration classes for string, range, object instance, collection and custom object

Pattern

Iterator pattern

In object-oriented programming, the iterator pattern is a design pattern in which an iterator is used to traverse a container and access the container’s elements. The iterator pattern decouples algorithms from containers; in some cases, algorithms are necessarily container-specific and thus cannot be decoupled.

In 4D using iterator provided by this component

While ($it.hasNext())
  $aValue:=$it.next()
  // do something
End while 

Usage

You can iterate over different type using the same way

Range

Iterate over a range of numeric

$it:=it .Range.new(1;7)
While ($it.hasNext())
	$value:=$it.next() //1, then 2, ..., until 7

End while 

it .Range.new(1;7).toCollection() // New collection(1;2;3;4;5;6;7)

String

Iterate over string characters, transform it to collection

it .StringIterator.new("Hello World").toCollection() // New collection("H";"e";"l";"l";"o";" ";"W";"o";"r";"l";"d")

eq. of [..."Hello World"] in some languages

Collection & Selection

There is different type of iterator provided, to traverse a collection, an object keys, or values or entries or even custom algorithms.

Type	Description
it.CollectionIterator	Iterate over a collection
it.SelectionIterator	Iterate over a selection
it.ObjectEntryIterator	Iterate over an object entries collection
it.ObjectKeyIterator	Iterate over an object keys collection
it.ObjectValueIterator	Iterate over an object values collection

See some usage in tests

Formula

Type	Description
it.IterableIterator	Iterate on object which implements two formula: length()->int and getValueAt(index)->value

Go further

4D Tags

You can use pass an iterable to PROCESS 4D TAGS, the template will be easier to read

<!--#4DLOOP ($1.hasNext())-->
<!--#4DEVAL $value:=$1.next()-->
<!--#4DENDLOOP-->

language features?

If a class have a function iterator which return an Iterator instance, we could imagine For each language keyword work with it, instead of keys browsing

---