Using Default Arguments in a Function

Question

I am confused about default values for PHP functions  Say I have a function like this   function foo  blah   x    some value    y    some other value            code here      What if I want to use the default argument for  x and set a different argument for  y    I have been experimenting with different ways and I am just getting more confused  For example  I tried these two   foo  blah   null   test    foo  blah        test      But both of those do not result in a proper default argument for  x  I have also tried to set it by variable name   foo  blah    x   y    test         I fully expected something like this to work  But it doesn t work as I expected at all  It seems like no matter what I do  I am going to have to end up typing in the default arguments anyway  every time I invoke the function  And I must be missing something obvious

User · Answer

lt  php function info  name  George   age 18    echo   name is  age years old  lt br gt      info           prints default values number of values   2  info  Nick         changes first default argument from George to Nick info  Mark  17         changes both default arguments  values    gt

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My 2 cents with null coalescing operator     since PHP 7   function foo  blah   x   null   y   null         varX    x     Default value X        varY    y     Default value Y                  You can check more examples on my repl it

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Pass an array to the function  instead of individual parameters and use null coalescing operator  PHP 7     Below  I m passing an array with 2 items  Inside the function  I m checking if value for item1 is set  if not assigned default vault    args     item2    gt   item2            item3    gt   value3         function function name   args            isset  args  item1       args  item1      default value

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In PHP 8 we can use named arguments for this problem  So we could solve the problem described by the original poster of this question   What if I want to use the default argument for  x and set a different argument for  y   With  foo blah   quot blah quot   y   quot test quot     Reference  https   wiki php net rfc named params  in particular the  quot Skipping defaults quot  section

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Optional arguments only work at the end of a function call  There is no way to specify a value for  y in your function without also specifying  x  Some languages support this via named parameters  VB C  for example   but not PHP   You can emulate this if you use an associative array for parameters instead of arguments -- i e   function foo array  args   array           x    isset  args  x       default x value     args  x         y    isset  args  y       default y value     args  y                 Then call the function like so   foo array  y    gt   my value

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This is case  when object are better - because you can set up your object to hold x and y   set up defaults etc    Approach with array is near to create object   In fact  object is bunch of parameters and functions which will work over object  and function taking array will work over some bunch ov parameters    Cerainly you can always do some tricks to set null or something like this as default

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You can also check if you have an empty string as argument so you can call like   foo  blah        non-default y value   null    Below the function   function foo  blah   x   null   y   null   z   null        if  null      x            x             x    some value              if  null      y            y             y    some other value              if  null      z            z             z    some other value              code here       It doesn t matter if you fill null or     you will still get the same result

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You can t do this directly  but a little code fiddling makes it possible to emulate   function foo  blah   x   false   y   false      if    x   x    some value     if    y   y    some other value         code

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It is actually possible  foo   blah    new ReflectionFunction  foo   - gt getParameters   1 - gt getDefaultValue     test     Whether you would want to do so is another story     UPDATE  The reasons to avoid this solution are   it is  arguably  ugly it has an obvious overhead  as the other answers proof  there are alternatives  But it can actually be useful in situations where   you don t want can t change the original function   you could change the function but   using null  or equivalent  is not an option  see DiegoDD s comment  you don t want to go either with an associative or with func num args   your life depends on saving a couple of LOCs    About the performance  a very simple test shows that using the Reflection API to get the default parameters makes the function call 25 times slower  while it still takes less than one microsecond  You should know if you can to live with that  Of course  if you mean to use it in a loop  you should get the default value beforehand

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The only way I know of doing it is by omitting the parameter  The only way to omit the parameter is to rearrange the parameter list so that the one you want to omit is after the parameters that you HAVE to set  For example   function foo  blah   y    some other value    x    some value     Then you can call foo like   foo  blah    test      This will result in    blah    blah    y    test    x    some value

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I would propose changing the function declaration as follows so you can do what you want  function foo  blah   x   null   y   null        if  null      x             x    quot some value quot              if  null      y             y    quot some other value quot              code here      This way  you can make a call like foo  blah   null   non-default y value    and have it work as you want  where the second parameter  x still gets its default value  With this method  passing a null value means you want the default value for one parameter when you want to override the default value for a parameter that comes after it  As stated in other answers   default parameters only work as the last arguments to the function  If you want to declare the default values in the function definition  there is no way to omit one parameter and override one following it   If I have a method that can accept varying numbers of parameters  and parameters of varying types  I often declare the function similar to the answer shown by Ryan P  Here is another example  this doesn t answer your question  but is hopefully informative  public function   construct  params   null        if   params instanceof SOMETHING               single parameter  of object type SOMETHING       elseif  is string  params                single argument given as string       elseif  is array  params                params could be an array of properties like array  x    gt   x1    y    gt   y1         elseif  func num args      3             args   func get args                3 parameters passed       elseif  func num args      5             args   func get args               5 parameters passed       else           throw new  InvalidArgumentException  quot Could not figure out parameters  quot

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function image array  img         defaults   array           src       gt   cow png            alt       gt   milk factory            height    gt  100           width     gt  50              img   array merge  defaults   img

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I recently had this problem and found this question and answers   While the above questions work  the problem is that they don t show the default values to IDEs that support it  like PHPStorm      if you use null you won t know what the value would be if you leave it blank   The solution I prefer is to put the default value in the function definition also   protected function baseItemQuery BoolQuery  boolQuery   limit 1000   sort        offset   0   remove dead true        if   limit   null   limit  1000      if   sort   null   sort           if   offset   null   offset   0            The only difference is that I need to make sure they are the same - but I think that s a small price to pay for the additional clarity

[php] Using Default Arguments in a Function

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