Elvis operator

<h2 id="alternative-syntaxes">Alternative syntaxes</h2>
In several languages, such as <a href="/facts/Common_Lisp/mq1pRbSF">Common Lisp</a>, <a href="/facts/Clojure/3JRNxKXx">Clojure</a>, <a href="/facts/Lua_(programming_language)/xkBCgta0">Lua</a>, <a href="/facts/Object_Pascal/cuGkuISv">Object Pascal</a>, <a href="/facts/Python_(programming_language)/YbuGqofa">Python</a>, <a href="/facts/Ruby_(programming_language)/BeYSaPSR">Ruby</a>, and <a href="/facts/JavaScript/XhhIIEsl">JavaScript</a>, there is no need for the Elvis operator, because the language's <a href="/facts/Logical_disjunction/jbI2EGlM">logical disjunction</a> operator (typically || or or) is <a href="/facts/Short-circuit_evaluation/GYhompFd">short-circuiting</a> and returns its first operand if it would evaluate to a <a href="/facts/Truthy_(computing)/SY4e2w8l">truthy value</a>, and otherwise its second operand, which may be a truthy or falsy value (rather than a <a href="/facts/Boolean_data_type/0GWYLDoC">Boolean true or false value</a>, such as in C and C++). These semantics are identical to the Elvis operator.

<h2 id="example">Example</h2>
<h3>Boolean variant</h3>
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 <a href="/facts/%253F%3a/3C8mgMD9">conditional ternary operator</a>:

 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.

<h3>Object reference variant</h3>
Main article: <a href="/facts/Null_coalescing_operator/U1T9KMKJ">null coalescing operator</a>
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" 
<h2 id="languages-supporting-the-elvis-operator">Languages supporting the Elvis operator</h2>
<ul><li>In GNU <a href="/facts/C_(programming_language)/Ky2No763">C</a> and <a href="/facts/C%252B%252B/Et0F2qn9">C++</a> (that is: in C and C++ with <a href="/facts/GNU_Compiler_Collection/t07jh01k">GCC</a> extensions), the second operand of the ternary operator is optional.<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a> This has been the case since at least GCC 2.95.3 (March 2001), and seems to be the original Elvis operator.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a></li>
<li>In <a href="/facts/Groovy_(programming_language)/vGAckbte">Apache Groovy</a>, the "Elvis operator" ?: is documented as a distinct operator;<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> this feature was added in Groovy 1.5<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a> (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.</li>
<li>In <a href="/facts/PHP/vU6YRJX0">PHP</a>, it is possible to leave out the middle part of the ternary operator since PHP 5.3.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> (June 2009).</li>
<li>The <a href="/facts/Fantom_(programming_language)/pgpD7oBN">Fantom</a> programming language has the ?: binary operator that compares its first operand with null.</li>
<li>In <a href="/facts/Kotlin_(programming_language)/CrAqIFLn">Kotlin</a>, the Elvis operator returns its left-hand side if it is not null, and its right-hand side otherwise.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> A common pattern is to use it with return, like this: val foo = bar() ?: return</li>
<li>In <a href="/facts/Gosu_(programming_language)/F9NH7mGC">Gosu</a>, the ?: operator returns the right operand if the left is null as well.</li>
<li>In <a href="/facts/C_Sharp_(programming_language)/UC2gxeyb">C#</a>, the <a href="/facts/Safe_navigation_operator/L7GdyDVo">null-conditional</a> operator, ?. is referred to as the "Elvis operator",<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> but it does not perform the same function. Instead, the <a href="/facts/Null-coalescing_operator/U1T9KMKJ">null-coalescing operator</a> ?? does.</li>
<li>In <a href="/facts/ColdFusion/4WB5vcA2">ColdFusion</a> and <a href="/facts/CFML/AbjNUunm">CFML</a>, the Elvis operator was introduced using the ?: syntax.</li>
<li>The <a href="/facts/Xtend/SrBn7sqm">Xtend</a> programming language has an Elvis operator.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a></li>
<li>In Google's <a href="/facts/Google_Closure_Tools/qs8FBWkj">Closure Templates</a>, the Elvis operator is a <a href="/facts/Null_coalescing_operator/U1T9KMKJ">null coalescing operator</a>, equivalent to isNonnull($a) ? $a : $b.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a></li>
<li>In <a href="/facts/Ballerina_(programming_language)/DLYoF1YB">Ballerina</a>, the Elvis operator L ?: R returns the value of L if it's not nil. Otherwise, return the value of R.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a></li>
<li>In <a href="/facts/JavaScript/XhhIIEsl">JavaScript</a>, 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.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a></li></ul>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/%253F%3a/3C8mgMD9">?:</a> or <a href="/facts/Conditional_operator/tB0uYuw0">conditional operator</a>, when used as a <a href="/facts/Ternary_operator/u1byWRfT">ternary operator</a></li>
<li><a href="/facts/Safe_navigation_operator/L7GdyDVo">Safe navigation operator</a>, often ?.</li>
<li><a href="/facts/Spaceship_operator/3yHfCsLS">Spaceship operator</a> <=></li>
<li><a href="/facts/Option_type/B0QX5wGB">Option type</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Joyce Farrell (7 February 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. <a href="978-1285081953" target="_blank">978-1285081953</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">"?? Operator". C# Reference. Microsoft. Retrieved 5 December 2018. <a href="https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-coalescing-operator" target="_blank">https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-coalescing-operator</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">"Conditional expressions". Dart Language. Google. <a href="https://dart.dev/language/operators#conditional-expressions" target="_blank">https://dart.dev/language/operators#conditional-expressions</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">"Using the GNU Compiler Collection (GCC): Conditionals with omitted operands". gcc.gnu.org. <a href="https://gcc.gnu.org/onlinedocs/gcc/extensions-to-the-c-language-family/conditionals-with-omitted-operands.html" target="_blank">https://gcc.gnu.org/onlinedocs/gcc/extensions-to-the-c-language-family/conditionals-with-omitted-operands.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">"Using and Porting the GNU Compiler Collection (GCC): C Extensions". gcc.gnu.org. <a href="https://gcc.gnu.org/onlinedocs/gcc-2.95.3/gcc_4.html#SEC70" target="_blank">https://gcc.gnu.org/onlinedocs/gcc-2.95.3/gcc_4.html#SEC70</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">"Elvis Operator (?: )". <a href="http://docs.groovy-lang.org/latest/html/documentation/index.html#_elvis_operator" target="_blank">http://docs.groovy-lang.org/latest/html/documentation/index.html#_elvis_operator</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">"The Apache Groovy programming language - Groovy 1.5 release notes". groovy-lang.org. <a href="http://groovy-lang.org/releasenotes/groovy-1.5.html" target="_blank">http://groovy-lang.org/releasenotes/groovy-1.5.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">"PHP: Comparison Operators - Manual". PHP website. Retrieved 2014-02-17. <a href="http://php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary" target="_blank">http://php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">"Null Safety - Kotlin Programming Language". Kotlin. <a href="https://kotlinlang.org/docs/reference/null-safety.html#elvis-operator" target="_blank">https://kotlinlang.org/docs/reference/null-safety.html#elvis-operator</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Albahari, Joseph; Albahari, Ben (2015). C# 6.0 in a Nutshell (6 ed.). O'Reilly Media. p. 59. ISBN 978-1491927069. <a href="978-1491927069" target="_blank">978-1491927069</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Efftinge, Sven. "Xtend - Expressions". eclipse.org. <a href="https://eclipse.org/xtend/documentation/203_xtend_expressions.html#elvis-operator" target="_blank">https://eclipse.org/xtend/documentation/203_xtend_expressions.html#elvis-operator</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">"Closure Templates - Expressions". GitHub. 29 October 2021. <a href="https://github.com/google/closure-templates/blob/master/documentation/reference/expressions.md#null-coalescing-operator--null-coalescing-operator" target="_blank">https://github.com/google/closure-templates/blob/master/documentation/reference/expressions.md#null-coalescing-operator--null-coalescing-operator</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">"Elvis Operator - Ballerina Programming Language". Ballerina. Archived from the original on 2018-12-20. Retrieved 2018-12-19. <a href="https://web.archive.org/web/20181220230754/https://ballerina.io/learn/by-example/elvis-operator.html" target="_blank">https://web.archive.org/web/20181220230754/https://ballerina.io/learn/by-example/elvis-operator.html</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">"Nullish coalescing operator (??) - JavaScript | MDN". developer.mozilla.org. Retrieved 2023-01-05. <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing" target="_blank">https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
</ol>

Elvis operator open-in-new

Elvis operator