Safe navigation operator
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object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of '' objects''. Objects can contain data (called fields, attributes or properties) and have actions they can perform (called procedures or methods and impl ...
, the safe navigation operator (also known as optional chaining operator, safe call operator, null-conditional operator, null-propagation operator) is a binary operator that returns
null Null may refer to: Science, technology, and mathematics Astronomy *Nuller, an optical tool using interferometry to block certain sources of light Computing *Null (SQL) (or NULL), a special marker and keyword in SQL indicating that a data value do ...
if its first argument is null; otherwise it performs a dereferencing operation as specified by the second argument (typically an object member access, array index, or lambda invocation). It is used to avoid sequential explicit null checks and assignments and replace them with method/property chaining. In programming languages where the navigation operator (e.g. ".") leads to an error if applied to a null object, the safe navigation operator stops the evaluation of a method/field chain and returns null as the value of the chain expression. It was first used by Groovy 1.0 in 2007 and is currently supported in languages such as C#,
Swift Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIF ...
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TypeScript TypeScript (abbreviated as TS) is a high-level programming language that adds static typing with optional type annotations to JavaScript. It is designed for developing large applications and transpiles to JavaScript. It is developed by Micr ...
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Ruby Ruby is a pinkish-red-to-blood-red-colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapph ...
, Kotlin,
Rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH) ...
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JavaScript JavaScript (), often abbreviated as JS, is a programming language and core technology of the World Wide Web, alongside HTML and CSS. Ninety-nine percent of websites use JavaScript on the client side for webpage behavior. Web browsers have ...
, and others. There is currently no common naming convention for this operator, but safe navigation operator is the most widely used term. The main advantage of using this operator is that it avoids the pyramid of doom. Instead of writing multiple nested ifs, programmers can just use usual chaining, but add question mark symbols before dots (or other characters used for chaining). While the safe navigation operator and
null coalescing operator The null coalescing operator is a binary operator that is part of the syntax for a basic conditional expression in several programming languages, such as (in alphabetical order): C# since version 2.0, Dart since version 1.12.0, PHP since versi ...
are both null-aware operators, they are operationally different.


Examples


Apex

Safe navigation operator examples in Apex: a .aMethod().aField // Evaluates to null if a

null a aMethod()?.aField // returns null if a aMethod() evaluates to null String profileUrl = user.getProfileUrl()?.toExternalForm(); return ELECT Name FROM Account WHERE Id = :accId.Name;


C#

C# 6.0 and above have ?., the ''null-conditional member access operator'' (which is also called the ''Elvis operator'' by Microsoft and is not to be confused with the general usage of the term ''
Elvis operator In certain computer programming languages, the Elvis operator, often written ?:, is a binary operator that evaluates its first operand and returns it if its value is ''logically true'' (according to a language-dependent convention, in other word ...
'', whose equivalent in C# is ??, the
null coalescing operator The null coalescing operator is a binary operator that is part of the syntax for a basic conditional expression in several programming languages, such as (in alphabetical order): C# since version 2.0, Dart since version 1.12.0, PHP since versi ...
) and ?[], the ''null-conditional element access operator'', which performs a null-safe call of an indexer accessor, get accessor. If the type of the result of the member access is a value type, the type of the result of a null-conditional access of that member is a nullable version of that value type. The following example retrieves the name of the author of the first article in an array of articles (provided that each article has an Author member and that each author has an Name member), and results in null if the array is null, if its first element is null, if the Author member of that article is null, or if the Name member of that author is null. Note that an IndexOutOfRangeException is still thrown if the array is non-null but empty (i.e. zero-length). var name = articles? .Author?.Name; Calling a lambda requires callback?.Invoke(), as there is no null-conditional invocation (callback?() is not allowed). var result = callback?.Invoke(args);


Clojure

Clojure doesn't have true operators in the sense other languages uses it, but as it interoperable with Java, and has to perform object navigation when it does, the some-> macro can be used to perform safe navigation. (some-> article .author .name)


CoffeeScript

Existential operator: zip = lottery.drawWinner?().address?.zipcode


Crystal

Crystal supports the try safe navigation method name = article.try &.author.try &.name


Dart

Conditional member access operator:var name = article?.author?.name


Gosu

Null safe invocation operator: var name = article?.author?.name The null-safe invocation operator is not needed for class attributes declared as Gosu Properties: class Foo var foo: Foo = null // the below will evaluate to null and not return a NullPointerException var bar = foo.Bar


Groovy

Safe navigation operator and safe index operator: def name = article?.authors? name


JavaScript

Added in ECMAScript 2020, the optional chaining operator provides a way to simplify accessing values through connected objects when it's possible that a reference or function may be ''undefined'' or ''null''. Major desktop browsers have supported this since 2020, and most mobile browsers added support by 2024. const name = article?.authors?. .name const result = callback?.() It short-circuits the whole chain of calls on its right-hand side: in the following example, ''bar'' is not "accessed". null?.foo.bar


Kotlin

Safe call operator: val name = article?.author?.name


Objective-C

Normal navigation syntax can be used in most cases without regarding NULLs, as the underlying messages, when sent to NULL, is discarded without any ill effects. NSString *name = article.author name;


Perl 5

Perl 5 does not have this kind of operator, but a proposal for inclusion was accepted with the following syntax: my $name = $article?->author?->name;


PHP

The null safe operator was accepted for PHP 8: $name = $article?->author?->name;


Raku (Perl 6)

Safe method call: my $name = $article.?author.?name;


Ruby

Ruby supports the &. safe navigation operator (also known as the ''lonely operator'') since version 2.3.0: name = article&.author&.name


Rust

Rust provides a ? operator that can seem like a safe navigation operator. However, a key difference is that when ? encounters a None value, it doesn't evaluate to None. Instead, it behaves like a return statement, causing the enclosing function or closure to immediately return None. The Option methods map() and and_then() can be used for safe navigation, but this option is more verbose than a safe navigation operator: fn print_author(article: Option
) An implementation using ? will print nothing (not even "Author:") if article is None or article.unwrap().author is None. As soon as ? sees a None, the function returns. fn try_print_author(article: Option
) -> Option<()>


Scala

The null-safe operator in Scala is provided by the library Dsl.scala. val name = article.?.author.?.name : @ ? The @ ? annotation can be used to denote a nullable value. case class Tree(left: Tree @ ? = null, right: Tree @ ? = null, value: String @ ? = null) val root: Tree @ ? = Tree( left = Tree( left = Tree(value = "left-left"), right = Tree(value = "left-right") ), right = Tree(value = "right") ) The normal . in Scala is not null-safe, when performing a method on a null value. a ullPointerExceptionshould be thrownBy The exception can be avoided by using ? operator on the nullable value instead: root.?.right.?.left.?.value should be(null) The entire expression is null if one of ? is performed on a null value. The boundary of a null safe operator ? is the nearest enclosing expression whose type is annotated as @ ?. ("Hello " + ("world " + root.?.right.?.left.?.value)) should be("Hello world null") ("Hello " + (("world " + root.?.right.?.left.?.value.?): @ ?)) should be("Hello null") (("Hello " + ("world " + root.?.right.?.left.?.value.?)): @ ?) should be(null)


Swift

Optional chaining operator, subscript operator, and call: let name = article?.authors? name let result = protocolVar?.optionalRequirement?()


TypeScript

Optional chaining operator was included in the Typescript 3.7 release: let x = foo?.bar?. .baz();


Visual Basic .NET

Visual Basic 14 and above have the ?. (the ''null-conditional member access operator'') and ?() (the ''null-conditional index operator''), similar to C#. They have the same behavior as the equivalent operators in C#. The following statement behaves identically to the C# example above. Dim name = articles?(0)?.Author?.Name


See also

*
Elvis operator In certain computer programming languages, the Elvis operator, often written ?:, is a binary operator that evaluates its first operand and returns it if its value is ''logically true'' (according to a language-dependent convention, in other word ...
*
Null coalescing operator The null coalescing operator is a binary operator that is part of the syntax for a basic conditional expression in several programming languages, such as (in alphabetical order): C# since version 2.0, Dart since version 1.12.0, PHP since versi ...


References

{{Reflist


External links


PEP 505
discussing the possibility of safe navigation operators for Python Operators (programming) Conditional constructs Articles with example code