PHP ternary operator vs null coalescing operator

Question

Can someone explain the differences between ternary operator shorthand      and null coalescing operator      in PHP   When do they behave differently and when in the same way  if that even happens     a     b   VS    a     b

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Ran the below on php interactive mode  php -a on terminal   The comment on each line shows the result  var export  false     value2         false var export  true      value2         true var export  null      value2         value2 var export            value2          quot  quot  var export  0         value2         0  var export  false     value2         value2 var export  true      value2         true var export  null      value2         value2 var export            value2         value2 var export  0         value2         value2  The Null Coalescing Operator        is like a  quot gate quot  that only lets NULL through  So  it always returns first parameter  unless first parameter happens to be NULL  This means    is same as    isset      is null      Use of     shorten  isset      is null    check e g  object    object    new objClassName     Stacking Null Coalese Operator          v    x     y     z               This is a sequence of  quot SET  amp  amp  NOT NULL quot s           if   x   amp  amp    is null  x                  return  x             else if   y  amp  amp   is null  y                  return  y             else                return  z               The Ternary Operator        is like a gate that lets anything falsy through - including NULL Anything falsy  0  empty string  NULL  false   isset    empty   Same like old ternary operator  X   Y   Z Note     will throw PHP NOTICE on undefined  unset or  isset    variables  Use of     checking empty     isset    is null   etc shorten ternary operation like  empty  x     x    y  to  x     y shorten if   x    echo  x    else   echo  y    to echo  x     y  Stacking Ternary Operator         echo 0    1    2    3    1         echo 1    0    3    2    1         echo 2    1    0    3    2         echo 3    2    1    0    3              echo 0    1    2    3    1         echo 0    0    2    3    2         echo 0    0    0    3    3                  Source  amp  Credit  http   php net manual en language operators comparison php 95997                This is basically a sequence of             if  truthy              else if truthy              else if truthy                         else      Stacking both  we can shorten this          if  isset   GET  name     amp  amp   is null   GET  name                    name     GET  name              else if   empty  user name                    name    user name             else                name    anonymous               To this           name     GET  name       user name     anonymous    Cool  right   -

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Both of them behave differently when it comes to dynamic data handling   If the variable is empty        the null coalescing will treat the variable as true but the shorthand ternary operator won t  And that s something to have in mind    a   NULL   c        print  a     1b   print   n    print  a     2b   print   n    print  c     1d   print   n    print  c     2d   print   n    print  e     1f   print   n    print  e     2f     And the output   1b 2b  2d 1f  Notice  Undefined variable  e in  in ZBAa1 on line 21 2f   Link  https   3v4l org ZBAa1

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The major difference is that      Ternary Operator expression  expr1    expr3 returns expr1 if expr1 evaluates to TRUE but on the other hand Null Coalescing Operator expression    expr1      expr2  evaluates to expr1 if expr1 is not NULL Ternary Operator expr1    expr3 emit a notice if the left-hand side value  expr1    does not exist but on the other hand Null Coalescing Operator  expr1      expr2  In particular  does not emit a notice if the left-hand side value  expr1    does not exist  just like isset       TernaryOperator is left associative      true    true    false     t     f      Null Coalescing Operator is right associative      a      b     c       Now lets explain the difference between by example      Ternary Operator          x      value   x    default   var dump  value       The above is identical to this if else statement if  x      value  x    else     value  default     var dump  value     Null Coalescing Operator        value   x    default   var dump  value       The above is identical to this if else statement if isset  x       value  x    else     value  default     var dump  value     Here is the table that explain the difference and similarity between      and               Special Note   null coalescing operator and ternary operator is an   expression  and that it doesn t evaluate to a variable  but to the   result of an expression  This is important to know if you want to   return a variable by reference  The statement return  foo     bar  and   return  var    42    a    b  in a return-by-reference function will   therefore not work and a warning is issued

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When using the superglobals like   GET or   REQUEST you should be aware that they could be an empty string  In this specal case this example   username     GET  user       nobody     will fail because the value of  username now is an empty string   So when using   GET or even   REQUEST you should use the ternary operator instead like this    username     empty   GET  user      GET  user    nobody     Now the value of  username is  nobody  as expected

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Null Coalescing operator performs just two tasks  it checks whether the variable is set and whether it is null  Have a look at the following example    lt  php   case 1   greeting    Hola   echo  greeting     Hi There     outputs   Hola     case 2   greeting   null  echo  greeting     Hi There     outputs   Hi There     case 3  unset  greeting   echo  greeting     Hi There     outputs   Hi There    The above code example states that Null Coalescing operator treats a non-existing variable and a variable which is set to NULL in the same way   Null Coalescing operator is an improvement over the ternary operator  Have a look at the following code snippet comparing the two    lt  php    example  checking for the   POST field that goes by the name of  fullname      in ternary operator echo  Welcome     isset   POST  fullname     amp  amp   is null   POST  fullname        POST  fullname      Mr  Whosoever       outputs  Welcome Mr  Whosoever    in null coalecing operator echo  Welcome       POST  fullname       Mr  Whosoever       outputs  Welcome Mr  Whosoever    So  the difference between the two is that Null Coalescing operator operator is designed to handle undefined variables better than the ternary operator  Whereas  the ternary operator is a shorthand for if-else   Null Coalescing operator is not meant to replace ternary operator  but in some use cases like in the above example  it allows you to write clean code with less hassle   Credits  http   dwellupper io post 6 php7-null-coalescing-operator-usage-and-examples

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Scroll down on this link and view the section  it gives you a comparative example as seen below    lt  php     Fetches the value of   GET  user   and returns  nobody  if it does not exist       username     GET  user       nobody       This is equivalent to       username   isset   GET  user        GET  user      nobody        Coalescing can be chained  this will return the first defined value out of   GET  user      POST  user    and  nobody        username     GET  user        POST  user       nobody     gt    However  it is not advised to chain the operators as it makes it harder to understand the code when reading it later on      The null coalescing operator      has been added as syntactic sugar for the common case of needing to use a ternary in conjunction with isset    It returns its first operand if it exists and is not NULL  otherwise it returns its second operand    Essentially  using the coalescing operator will make it auto check for null unlike the ternary operator

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If you use the shortcut ternary operator like this  it will cause a notice if   GET  username   is not set    val     GET  username       default     So instead you have to do something like this    val   isset   GET  username        GET  username      default     The null coalescing operator is equivalent to the above statement  and will return  default  if   GET  username   is not set or is null    val     GET  username       default     Note that it does not check truthiness  It checks only if it is set and not null   You can also do this  and the first defined  set and not null  value will be returned    val    input1     input2     input3     default     Now that is a proper coalescing operator

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When your first argument is null  they re basically the same except that the null coalescing won t output an E NOTICE when you have an undefined variable  The PHP 7 0 migration docs has this to say      The null coalescing operator      has been added as syntactic sugar   for the common case of needing to use a ternary in conjunction with   isset    It returns its first operand if it exists and is not NULL    otherwise it returns its second operand    Here s some example code to demonstrate this    lt  php   a   null   print  a     b      b print   n    print  a     b      b print   n    print  c     a      a print   n    print  c     a      Notice  Undefined variable  c in  in apAIb on line 14 print   n     b   array  a    gt  null    print  b  a       d      d print   n    print  b  a       d      d print   n    print  b  c       e      e print   n    print  b  c       e      Notice  Undefined index  c in  in apAIb on line 33 print   n     The lines that have the notice are the ones where I m using the shorthand ternary operator as opposed to the null coalescing operator  However  even with the notice  PHP will give the same response back   Execute the code  https   3v4l org McavC  Of course  this is always assuming the first argument is null  Once it s no longer null  then you end up with differences in that the    operator would always return the first argument while the    shorthand would only if the first argument was truthy  and that relies on how PHP would type-cast things to a boolean   So    a   false     f      false  b   false     g       g    would then have  a be equal to false and  b equal to  g

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The other answers goes deep and give great explanations  For those who look for quick answer    a     fallback  is  a    a    fallback   while   a     fallback  is  a   isset  a     a    fallback     The main difference would be when the left operator is either    A falsy value that is NOT null  0      false            An undefined variable

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It seems there are pros and cons to using either    or     The pro to using    is that it evaluates false and null and    the same  The con is that it reports an E NOTICE if the preceding argument is null  With    the pro is that there is no E NOTICE  but the con is that it does not evaluate false and null the same  In my experience  I have seen people begin using null and false interchangeably but then they eventually resort to modifying their code to be consistent with using either null or false  but not both  An alternative is to create a more elaborate ternary condition   isset  something  or   something     something    something else   The following is an example of the difference of using the    operator using both null and false     false   null   var    false     true   echo  var    --- lt br gt     returns  true---   false   false   var    false     true   echo  var    --- lt br gt      returns  ---   By elaborating on the ternary operator however  we can make a false or empty string    behave as if it were a null without throwing an e notice    false   null   var    isset  false  or   false     false    true   echo  var    --- lt br gt     returns  ---   false   false   var    isset  false  or   false     false    true   echo  var    --- lt br gt     returns  ---   false        var    isset  false  or   false     false    true   echo  var    --- lt br gt     returns  ---   false   true   var    isset  false  or   false     false    true   echo  var    --- lt br gt     returns  1---   Personally  I think it would be really nice if a future rev of PHP included another new operator     that replaced the above syntax  ie      var    false     true   That syntax would evaluate null  false  and    equally and not throw an E NOTICE

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class a       public  a    aaa       a   new a     echo  a- gt a      Writes  aaa  echo  a- gt b      Notice  Undefined property  a   b  echo  a- gt a      a- gt a does not exists       Writes  aaa      Does not throw an error although  a- gt b does not exist  echo  a- gt b      a- gt b does not exist        Writes  a- gt b does not exist      Does not throw an error although  a- gt b and also  a- gt b- gt c does not exist  echo  a- gt b- gt c      a- gt b- gt c does not exist        Writes  a- gt b- gt c does not exist

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Both are shorthands for longer expressions      is short for  a    a    b  This expression will evaluate to  a if  a evaluates to TRUE      is short for isset  a     a    b  This expression will evaluate to  a if  a is set and not null   Their use cases overlaps when  a is undefined or null  When  a is undefined    will not produce an E NOTICE  but the results are the same  When  a is null the result is the same

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For the beginners   Null coalescing operator        Everything is true except null values and undefined  variable array index object attributes   ex    array        object   new stdClass     var export  false     second                                false var export  true      second                                true var export  null      second                                 second  var export            second                                   var export   some text         second                        some text  var export  0         second                                0 var export   undefinedVarible     second                     second  var export   array  undefined index       second             second  var export   object- gt undefinedAttribute     second           second    this is basically check the variable array index  object attribute   etc  is exist and not null  similar to isset function  Ternary operator shorthand        every false things  false null 0 empty string  are come as false  but if it s a undefined it also come as false but Notice will throw  ex   array        object   new stdClass     var export  false     second                                 second  var export  true      second                                true var export  null      second                                 second  var export            second                                 second  var export   some text         second                        some text  var export  0         second                                 second  var export   undefinedVarible     second                     second  Notice  Undefined variable     var export   array  undefined index       second             second  Notice  Undefined index     var export   object- gt undefinedAttribute     second           Notice  Undefined index       Hope this helps

[php] PHP ternary operator vs null coalescing operator

The Null Coalescing Operator `??`

Use of `??`

Stacking Null Coalese Operator

The Ternary Operator `?:`

Use of `?:`

Stacking Ternary Operator

Stacking both, we can shorten this:

To this:

Cool, right? :-)

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