Elvis operator (original) (raw)

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Binary operator in computer programming

This article is about the use of a ?: operator as a binary operator. For use as a ternary operator, see ?:.

Elvis Presley, whose hair resembles the operator viewed sideways

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 words, a truthy value), and otherwise evaluates and returns its second operand. The second operand is only evaluated if it is to be returned (short-circuit evaluation). The notation of the Elvis operator was inspired by the ternary conditional operator, [? :](/wiki/%3F: "?:"), since the Elvis operator expression A ?: B is approximately equivalent to the ternary conditional expression A ? A : B.

The name "Elvis operator" refers to the fact that when its common notation, ?:, is viewed sideways, it resembles an emoticon of Elvis Presley with his signature hairstyle.[1]

A similar operator is the null coalescing operator, where the boolean truth(iness) check is replaced with a check for non-null instead. This is usually written ??, and can be seen in languages like C#[2] or Dart.[3]

Alternative syntaxes

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In several languages, such as Common Lisp, Clojure, Lua, Object Pascal, Perl, Python, Ruby, and JavaScript, there is no need for the Elvis operator, because the language's logical disjunction operator (typically || or or) is short-circuiting and returns its first operand if it would evaluate to a truthy value, and otherwise its second operand, which may be a truthy or falsy value (rather than a Boolean true or false value, such as in C and C++). These semantics are identical to the Elvis operator.

In a language that supports the Elvis operator, something like this:

x = f() ?: g()

will set x equal to the result of f() if that result is truthy, and to the result of g() otherwise.

It is equivalent to this example, using the conditional ternary operator:

x = f() ? f() : g()

except that it does not evaluate f() twice if it yields truthy. Note the possibility of arbitrary behaviour if f() is not a state-independent function that always returns the same result.

Object reference variant

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This code will result in a reference to an object that is guaranteed to not be null. Function f() returns an object reference instead of a boolean, and may return null, which is universally regarded as falsy:

x = f() ?: "default value"

Languages supporting the Elvis operator

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In GNU C and C++ (that is: in C and C++ with GCC extensions), the second operand of the ternary operator is optional.[4] This has been the case since at least GCC 2.95.3 (March 2001), and seems to be the original Elvis operator.[5]
In Apache Groovy, the "Elvis operator" ?: is documented as a distinct operator;[6] this feature was added in Groovy 1.5[7] (December 2007). Groovy, unlike GNU C and PHP, does not simply allow the second operand of ternary ?: to be omitted; rather, binary ?: must be written as a single operator, with no whitespace in between.
In PHP, it is possible to leave out the middle part of the ternary operator since PHP 5.3.[8] (June 2009).
The Fantom programming language has the ?: binary operator that compares its first operand with null.
In Kotlin, the Elvis operator returns its left-hand side if it is not null, and its right-hand side otherwise.[9] A common pattern is to use it with return, like this: val foo = bar() ?: return
In Gosu, the ?: operator returns the right operand if the left is null as well.
In C#, the null-conditional operator, ?. is referred to as the "Elvis operator",[10] but it does not perform the same function. Instead, the null-coalescing operator ?? does.
In ColdFusion and CFML, the Elvis operator was introduced using the ?: syntax.
The Xtend programming language has an Elvis operator.[11]
In Google's Closure Templates, the Elvis operator is a null coalescing operator, equivalent to isNonnull($a) ? <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo>:</mo></mrow><annotation encoding="application/x-tex">a : </annotation></semantics></math>a:b.[12]
In Ballerina, the Elvis operator L ?: R returns the value of L if it's not nil. Otherwise, return the value of R.[13]
In JavaScript, the nullish coalescing (??) operator is a logical operator that returns its right-hand side operand when its left-hand side operand is null or undefined, and otherwise returns its left-hand side operand.[14]
In Perl there is a logical short-circuiting disjunction || and a similar lower precedence or.[15] They differ from the bitwise or operator | which evaluates both operands without short-circuiting. There is also a corresponding assignment operator ||= that evaluates its right-hand operand and assigns it to the left-operand unless the logical value of the left-operand is true. There is also a short-circuiting defined-or operator // which evaluates its right-operand and returns its value only if the left-operand is undefined. Finally, the corresponding assignment operator is //=. Similar exclusive-or operators are not Elvis operators as they do not short-circuit. Other short-circuiting operators are the logical-and ones && and and, but their behavior is opposite that of the Elvis operator.
?: or conditional operator, when used as a ternary operator
Null coalescing operator, ?? operator
Safe navigation operator, often ?.
Spaceship operator <=>
Option type

^ Joyce Farrell (February 7, 2013). Java Programming. Cengage Learning. p. 276. ISBN 978-1285081953. The new operator is called Elvis operator because it uses a question mark and a colon together (?:); if you view it sideways, it reminds you of Elvis Presley.
^ "?? Operator". C# Reference. Microsoft. Retrieved December 5, 2018.
^ "Conditional expressions". Dart Language. Google.
^ "Using the GNU Compiler Collection (GCC): Conditionals with omitted operands". gcc.gnu.org.
^ "Using and Porting the GNU Compiler Collection (GCC): C Extensions". gcc.gnu.org.
^ "Elvis Operator (?: )".
^ "The Apache Groovy programming language - Groovy 1.5 release notes". groovy-lang.org.
^ "PHP: Comparison Operators - Manual". PHP website. Retrieved February 17, 2014.
^ "Null Safety - Kotlin Programming Language". Kotlin.
^ Albahari, Joseph; Albahari, Ben (2015). C# 6.0 in a Nutshell (6 ed.). O'Reilly Media. p. 59. ISBN 978-1491927069.
^ Efftinge, Sven. "Xtend - Expressions". eclipse.org.
^ "Closure Templates - Expressions". GitHub. October 29, 2021.
^ "Elvis Operator - Ballerina Programming Language". Ballerina. Archived from the original on December 20, 2018. Retrieved December 19, 2018.
^ "Nullish coalescing operator (??) - JavaScript | MDN". developer.mozilla.org. Retrieved January 5, 2023.
^ "perlop". Retrieved July 9, 2025.