Seeking 'coalesce' php internal function View as Markdown

D.

Please read the mailing list archives. And don't mention it again ;)

• Steph

----- Original Message -----
From: "D. Dante Lorenso" dante@vocalspace.com
To: dante@lorenso.com
Cc: internals@lists.php.net
Sent: Wednesday, May 03, 2006 8:05 AM
Subject: Re: [PHP-DEV] Seeking 'coalesce' php internal function

D. Dante Lorenso wrote:

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");

I mean "I DON'T think like this CAN be written in userspace". And, yes,
there is a bug in that code up above (around $_GET testing), but the
'coalesce' function removes the test/set with identical values so
removes those kinds of careless bugs.

Dante

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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

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

The default value for 'filled()' if all values test TRUE for empty()
should be FALSE, not NULL. This is more consistent with the return
values of empty().

Since filled() returns the first non-empty() value in the list of
parameters provided, it works well when cast into a boolean context
because the non-empty() value should evaluate as TRUE. Example:

filled("testing") // returns testing
if (filled("testing")) {} // true
filled(87) // returns 87
(boolean) filled(87) // true

$x["apple"] = "42";
filled($x["apple"]) // returns 42
filled($x["pear"]) // returns false
if (filled($x["apple"]) !== false) {} // true
if (filled($x["pear"]) !== false) {} // false

Just wanted to chime in with an update in case 'filled()' can actually
be considered. I'd like everyone to consider this one function to be
evaluated on it's merits alone and apart from any other functions which
also might be wanted. filled() is the opposite of empty() and is not
dealing with tests for 'isset()'. Another function should be proposed
to solve that problem if it would still be needed after filled() is
implemented.

Do I have any power to call a vote on this?

Dante

D. Dante Lorenso wrote:

Dear Internals,

I'd like a white bikeshed, but until you can decide on a color, how
about we just build the bikeshed already. Please consider the
following specification:

========== 8< ==================== 8< ==================== 8< ==========

filled

(PHP 5.2.0)

filled - Find first non-empty value in a variable list where empty()
evaluates as FALSE.

Description

mixed filled ( mixed varname [, mixed ...] )

filled() takes a variable number of parameters. For each of these,
filled() looks for a variable where !empty( varname ) evaluates as
TRUE. It returns the first non-empty value or NULL if all values are
empty().

Note: filled() only checks variables as anything else will result in a
parse error. In other words, the following will not work:
filled(trim($name)).
filled() is the opposite of empty(), and no warning is generated
when any one of the variables is not set.

Return Values

Returns first non-empty() value.

If all values are empty(), returns NULL.

Example

<?php
echo filled($x["somekey"], $_GET["getkey"], $default, "example");
echo filled("yes"); // prints yes
filled(false); // returns NULL
echo filled($x["apple"], $y, "banana"); // prints banana
$y = "cat";
echo filled($x["apple"], $y, "banana"); // prints cat
$x["apple"] = "pear";
echo filled($x["apple"], $y, "banana"); // prints pear
unset($x["apple"]);
echo filled($x["apple"], $y, "banana"); // prints cat
?>

See also empty()

========== 8< ==================== 8< ==================== 8< ==========

Dante