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Date: Wed, 03 May 2006 02:13:44 -0500
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To: Johannes Schlueter <johannes@php.net>
Cc: internals@lists.php.net, dante@lorenso.com
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Subject: Re: [PHP-DEV] Seeking 'coalesce' php internal function
From: dante@vocalspace.com ("D. Dante Lorenso")

Johannes Schlueter wrote:
> please search the archives for "ifsetor".
>   

I have completed this search and find:

    http://marc.theaimsgroup.com/?r=1&w=2&q=b&l=php-dev&s=coalesce
    http://marc.theaimsgroup.com/?l=php-dev&w=2&r=1&s=ifsetor&q=b

I am using PHP 5.1.2 currently and thought using pass-by-reference was 
frowned upon.  Assuming a mistaken assumption I move forward and see the 
following code which was presented to the list:

<?php
function ifsetor(&$var, $value) {
    return (isset($var)) ? $var : $value;
}
print ifsetor($x, "dante");
?>

This works as I'd like in my dev environment, however, this does not 
solve the problem of allowing variable number of parameters (variables 
and values).  So, I've whipped up this 10 variable version:

<?php
function ifsetor(&$var1, &$var2, &$var3, &$var4, &$var5, &$var6, &$var7, 
&$var8, &$var9, &$var10) {
    if (isset($var1)) return $var1;
    if (isset($var2)) return $var2;
    if (isset($var3)) return $var3;
    if (isset($var4)) return $var4;
    if (isset($var5)) return $var5;
    if (isset($var6)) return $var6;
    if (isset($var7)) return $var7;
    if (isset($var8)) return $var8;
    if (isset($var9)) return $var9;
    if (isset($var10)) return $var10;
    return false;
}
print ifsetor($x["notset"]->notset, $y["notset"]->notset, $z->notset, 
"dante");
?>

PHP Fatal error:  Only variables can be passed by reference in 
.../ifsetor.php on line 15
PHP Warning:  Missing argument 5 for ifsetor(), called in 
.../ifsetor.php on line 15 and defined in .../ifsetor.php on line 2
PHP Warning:  Missing argument 6 for ifsetor(), called in 
.../ifsetor.php on line 15 and defined in .../ifsetor.php on line 2
PHP Warning:  Missing argument 7 for ifsetor(), called in 
.../ifsetor.php on line 15 and defined in .../ifsetor.php on line 2
PHP Warning:  Missing argument 8 for ifsetor(), called in 
.../ifsetor.php on line 15 and defined in .../ifsetor.php on line 2
PHP Warning:  Missing argument 9 for ifsetor(), called in 
.../ifsetor.php on line 15 and defined in .../ifsetor.php on line 2
PHP Warning:  Missing argument 10 for ifsetor(), called in 
.../ifsetor.php on line 15 and defined in .../ifsetor.php on line 2

I can work around passing values by reference by calling the function 
like this:

    print ifsetor($x["notset"]->notset, $y["notset"]->notset, 
$z->notset, $temp = "dante");

But you have to admit that's getting ugly and still, there are undefined 
parameters declared ... so then I tried it by assigning default values:

<?php
function ifsetor(&$var1=null, &$var2=null, &$var3=null, &$var4=null, 
&$var5=null, &$var6=null, &$var7=null, &$var8=null, &$var9=null, 
&$var10=null) {
    if (isset($var1)) return $var1;
    if (isset($var2)) return $var2;
    if (isset($var3)) return $var3;
    if (isset($var4)) return $var4;
    if (isset($var5)) return $var5;
    if (isset($var6)) return $var6;
    if (isset($var7)) return $var7;
    if (isset($var8)) return $var8;
    if (isset($var9)) return $var9;
    if (isset($var10)) return $var10;
    return false;
}
print ifsetor($x["notset"]->notset, $y["notset"]->notset, $z->notset, 
$temp = "dante")."\n";
print_r($x);
?>

Now, $x, $y, and $z ARE set ...

    dante
    Array ( [notset] => stdClass Object ( [notset] => ) )

This is a nasty side-effect and can not be accepted.  I did not want to 
set these variables, just check their existance.

I am willing to go away and concede that this should be done in 
userspace IF you can show me that it is in fact possible.  The 2 
argument ifsetor is trivial in userspace, yes, but the variable case is 
more useful in a variety of situations and provides the most benefit to 
simplify code.  I did not find the answer in the archives.  Can you 
point me in the right direction?  I need to be able to do all of the 
following:

    * variable number of parameters
    * test 'isset' or 'empty'
    * testing variables and non-variable values (pass-by-reference won't
      work on values)
    * not have side-effect of defining values which are not already set
    * not trigger notices or warnings
    * returns value of first proper match

Dante

> johannes
>
> On Wednesday 03 May 2006 07:56, D. Dante Lorenso wrote:
>   
>> All,
>>
>> I'm sure this has been asked somewhere, but since I see requests for
>> features for 5.2 or 6.0, I'd like to add a "simple" item to the list
>> which would be quite useful to me and would simplify and clean up a lot
>> of code out there:
>>
>>     function coalesce(...)
>>
>> This works much like in the SQL version of the same.  In SQL, the
>> function returns the first non-null argument from an arbitrary list.  In
>> our use, it should return the first non-empty value from the list:
>>
>> Example:
>>
>>     $x = "dante";
>>     $y = "";
>>     $z = "";
>>
>>     $value = coalesce($z, $y, $x); // $value = "dante"
>>
>> This function would ideally be built into the language and bypass
>> warnings about undefined variables like 'empty' does.  It might be nice
>> to have several varieties of this function:
>>
>>     * return first parameter where empty() is FALSE
>>     * return first parameter where isset() is TRUE
>>
>> I don't think something like this can NOT be written in userspace
>> because the 'isset' and 'empty' checks need to be run before arguments
>> can be passed to a user function or warnings will start flying.  A
>> function like this simplifies code which used to look like this:
>>
>>     if (!empty($_POST["postkey"])) {
>>         $value = $_POST["postkey"];
>>     }
>>     elseif (!empty($_GET["getkey"])) {
>>         $value = $_POST["getkey"];
>>     }
>>     elseif (!empty($default_value)) {
>>         $value = $default_value;
>>     }
>>     else {
>>         $value = "hard coded value";
>>     }
>>
>> Into this:
>>
>>     $value = coalesce($_POST["postkey"], $_GET["getkey"],
>> $default_value, "hard coded value");
>>
>> Can this be built and included?
>>
>> Dante
>>     
>
>