2.6 KiB
^title Lists
A list is a compound object that holds a collection of elements identified by integer index. You can create a list by placing a sequence of comma-separated expressions inside square brackets:
:::dart
[1, "banana", true]
Here, we've created a list of three elements. Notice that the elements don't have to be the same type.
Accessing Elements
You can access an element from a list by calling the subscript operator on it with the index of the element you want. Like most languages, indexes start at zero:
:::dart
var hirsute = ["sideburns", "porkchops", "'stache"]
hirsute[0] // "sideburns".
hirsute[1] // "porkchops".
Negative indices counts backwards from the end:
:::dart
hirsute[-1] // "'stache".
hirsute[-2] // "porkchops".
It's a runtime error to pass an index outside of the bounds of the list. If you don't know what those bounds are, you can find out using count:
:::dart
hirsute.count // 3.
Adding elements
Lists are mutable, meaning their contents can be changed. You can swap out an existing element in the list using the subscript setter:
:::dart
hirsute[1] = "muttonchops"
IO.print(hirsute[1]) // muttonchops.
It's an error to set an element that's out of bounds. To grow a list, you can use add to append a single item to the end:
:::dart
hirsute.add("goatee")
IO.print(hirsute.count) // 4.
You can insert a new element at a specific position using insert:
:::dart
hirsute.insert("soul patch", 2)
The first argument is the value to insert, and the second is the index to insert it at. All elements following the inserted one will be pushed down to make room for it.
It's valid to "insert" after the last element in the list, but only right after it. Like other methods, you can use a negative index to count from the back. Doing so counts back from the size of the list after it's grown by one:
:::dart
var letters = ["a", "b", "c"]
letters.insert("d", 3) // OK: inserts at end.
IO.print(letters) // ["a", "b", "c", "d"]
letters.insert("e", -2) // Counts back from size after insert.
IO.print(letters) // ["a", "b", "c", "e", "d"]
Removing elements
The opposite of insert is removeAt. It removes a single element from a given position in the list. All following items are shifted up to fill in the gap:
var letters = ["a", "b", "c"]
letters.removeAt(1)
IO.print(letters) // ["a", "c"]
If you want to remove everything from the list, you can clear it:
hirsute.clear
IO.print(hirsute) // []
TODO: Ranges, iteration, etc.