PHP: Inserting a link into an array?

Question

I am trying to insert into an array at some point:

$hi = "test"; $var2 = "next"; $arr = array(&$hi); $arr[] = &$var2; // this works array_splice($arr, 1, 0, &$var2); // this doesn't 

Why is trying to insert it into an array with a splicing error and using the first method not working?

Answer 1

A quick and dirty answer, but remember that calling this function with a link is outdated and may (depending on your php configuration) generate a warning:

 array_splice($arr, 1, 0, array(&$var2)); 

Response to impressions and answers: what happens is pretty subtle. When you do the splice because you inserted the link at this position, $ var2 is really reassigned. You can check it with the following code:

 <?php $hi = "test"; $var2 = "next"; $arr = array(&$hi); $arr[] = &$var2; // this works printf("=== var2 before splice:\n%s\n", var_export($var2, TRUE)); array_splice($arr, 1, 0, &$var2); // this doesn't printf("=== var2 after splice:\n%s\n", var_export($var2, TRUE)); ?> 

You will get the following result:

 === var2 before splice: 'next' === var2 after splice: array ( 0 => 'next', ) 

Note that before splice, the string $ var2 was a string, as expected ("next"). However, after splicing, $ var2 was replaced by an array containing one element, the string "next".

I think the reason for this is because the documentation says: "If the replacement is not an array, it will look with one parameter (for example ((array) $"). So what happens:

• You pass & $ var2 to the array as a replacement.
• Internally, php will convert & $ var2 to an array (& $ var2). Actually, this can do something equivalent to $ param = array ($ param), which means that & $ var2 will be set to an array (& $ var2), and since this is a link, not a copy of $ var2 like this usually will, this affects a variable that usually goes beyond the scope of the call.
• Now he moves this new value of $ var2 to the end position and inserts a copy of $ var2 into the second position.

I'm not sure for sure that all the magic happens inside, but $ var is definitely reassigned during splicing. Note that if you use a third variable, because it does not assign something to something that already exists as a reference, it works as expected:

 <?php $hi = "test"; $var2 = "next"; $var3 = "last"; $arr = array(&$hi); $arr[] = &$var2; // this works array_splice($arr, 1, 0, &$var3); printf("=== arr is now\n%s\n", var_export($arr, TRUE)); ?> 

Generates the result:

 === arr is now array ( 0 => 'test', 1 => 'last', 2 => 'next', ) 

Answer 2

You may need to make the last argument an array, otherwise according to manual you will get typecasted to one.

 array_splice( $arr, 1, 0, array( &$var2 ) ); 

Answer 3

When I try to give an example similar to yours, I get a warning saying that the "Call-by-reference link is out of date". According to this answer :

You can set allow_call_time_pass_reference to true in the php.ini file. But it's a hack.

Answer 4

Here I repeat the array ($ values_arr) and save the links of each variable in another array ($ params). You can change its use according to your requirements.

 $params = array(); $values_arr = array('a', 'b', 123); foreach ($values_arr as $key=>&$val) { $params[$key] = &$val; } 

Result

 array (size=3) 0 => &string 'a' (length=1) 1 => &string 'b' (length=1) 2 => &int 123