Editing Immutable object (section)

=== Scala ===
In [[Scala (programming language)|Scala]], any entity (narrowly, a binding) can be defined as mutable or immutable: in the declaration, one can use <code>val</code> (value) for immutable entities and <code>var</code> (variable) for mutable ones. Note that even though an immutable binding can not be reassigned, it may still refer to a mutable object and it is still possible to call mutating methods on that object: the ''binding'' is immutable, but the underlying ''object'' may be mutable.

For example, the following code snippet:
<syntaxhighlight lang="scala">
val maxValue = 100
var currentValue = 1
</syntaxhighlight>
defines an immutable entity <code>maxValue</code> (the integer type is inferred at compile-time) and a mutable entity named <code>currentValue</code>.

By default, collection classes such as <code>List</code> and <code>Map</code> are immutable, so update-methods return a new instance rather than mutating an existing one. While this may sound inefficient, the implementation of these classes and their guarantees of immutability mean that the new instance can re-use existing nodes, which, especially in the case of creating copies, is very efficient.<ref>{{cite web|url=http://www.scala-lang.org/docu/files/collections-api/collections_12.html |title=Scala 2.8 Collections API – Concrete Immutable Collection Classes |publisher=Scala-lang.org |access-date=2014-04-14}}</ref>{{Better source|reason=This is a controversial (and vague) claim, so should be supported by a source other than the Scala foundation itself.|date=July 2017}}