operator the Elvis operator in PHP

Question

I saw this today in some PHP code    items    items     this- gt  handle- gt result  next    this- gt  result   this     I m not familiar with the    operator being used here  It looks like a ternary operator  but the expression to evaluate to if the predicate is true has been omitted  What does it mean

User · Answer

Be careful with arrays  We must write a checking variable after    because     params     param1    gt   value1                 param2    gt   value2                 param3    gt   value3         param1   isset  params  param1     null     param2    empty  params  param2     null     param3    params  param3    null     get E NOTICE  if  params  param3   eq false    var dump  param1  param2  param3     true    would like to expect  value1    true    would like to expect  value2    param3    properly  but problem above  Updated From RFC  In PHP 7 the operator Null Coalesce Operator will do it  for example   param1    params  param1      null     Equivalent to    param1   isset  params  param1       params  param1     null

User · Answer

Yes  this is new in PHP 5 3  It returns either the value of the test expression if it is evaluated as TRUE  or the alternative value if it is evaluated as FALSE

User · Answer

See the docs      Since PHP 5 3  it is possible to leave out the middle part of the ternary operator  Expression expr1    expr3 returns expr1 if expr1 evaluates to TRUE  and expr3 otherwise

User · Answer

Another important consideration  The Elvis Operator breaks the Zend Opcache tokenization process  I found this the hard way  While this may have been fixed in later versions  I can confirm this problem exists in PHP 5 5 38  with in-built Zend Opcache v7 0 6-dev    If you find that some of your files  refuse  to be cached in Zend Opcache  this may be one of the reasons    Hope this helps

User · Answer

It evaluates to the left operand if the left operand is truthy  and the right operand otherwise   In pseudocode   foo   bar    baz    roughly resolves to  foo   bar   bar   baz    or  if  bar        foo   bar    else       foo   baz      with the difference that bar will only be evaluated once   You can also use this to do a  self-check  of foo as demonstrated in the code example you posted   foo   foo    bar    This will assign bar to foo if foo is null or falsey  else it will leave foo unchanged   Some more examples    lt  php     var dump 5    0      5     var dump false    0      0     var dump null     foo        foo      var dump true    123      true     var dump  rock      roll        rock    gt    By the way  it s called the Elvis operator

User · Answer

Elvis operator     is the Elvis operator  This is a binary operator which does the following  Coerces the value left of    to a boolean and checks if it is true  If true it will return the expression on the left side  if false it will return the expression on the right side  Example  var dump 0     quot Expression not true quot           expression returns  Expression not true var dump  quot  quot      quot Expression not true quot          expression returns  Expression not true var dump  quot hi quot      quot Expression not true quot        expression returns string hi var dump null     quot Expression not true quot        expression returns  Expression not true var dump 56     quot Expression not true quot          expression return int 56  When to use  The Elvis operator is basically shorthand syntax for a specific case of the ternary operator which is   testedVar     testedVar    otherVar   The Elvis operator will make the syntax more consise in the following manner   testedVar     otherVar

[php] ?: operator (the 'Elvis operator') in PHP

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