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Asked: 2020-01-08 06:38:57 +0800 CST 2020-01-08 06:38:57 +0800 CST

Differences between the Elvis operator ?: and the null coalescing operator

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Reading this question I found a reference to the so-called Elvis operator (link in English) or ?:which is very similar to the operator ||used in javascript or also called the null coalescence operator (link in English).

Investigating more about both I could not distinguish any difference between them which led me to ask myself, is there really a difference? If there isn't, then why are there two references to something that semantically means the same thing?

Examples of the elvis operator

var variable = foo ?: bar

Returns fooif fooit exists and is not null else returnsbar

Null coalescing operator

var variable = foo || bar

which does exactly the same

Note: The elvis operator is not part of the javascript language, the ternary operator is instead .

operador

2 Answers

  1. Best Answer

    Both behave the same, but the difference is in which languages ​​you are using it.

    For example the Elvis Operatoris not available in Javascript, since for that we have the ||o double pipe.

    On the other hand, in PHP, for example, there is no || to perform Null Coalescing Operator and for this the ?:, simply a if ternarioor failing that the ??.

    If you look at the Wikipedia Article you post, and look at the languages ​​it's used it Elvis Operatorjust shows up. C, GroovyandPHP

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  2. Yes a = false,

    a ?? 'x'  ->  a
a || 'x'  ->  x

    In some languages ​​there are several false values ​​(usually they are false, null, 0, "", empty list, etc.). The null coalescing operator would return those values ​​if they are on the left side (except with null, of course), while the Elvis operator would return those on the other side.

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