This is a bit late to the party but I didn't see this answer and just recently implemented something similar for a debugging class ( to handle circular references). As you guys may or may not know the normal printing functions such as var_export, have limited or no circular reference support.
As noted the spl_object_hash is unique per instance, the problem I had with it is that it is ugly. Not really suited to printing for my debugger as it's something like this 000000006ac56bae0000000044fda36f which can be hard to compare to say this 000000006ac56bae0000000044fda35f. So like the OP stated what I wanted was just a number of the instance ( I only really needed this on a per class basis ).
Therefor the simple solution for me was to do the following.
$class = get_class( $input );
$hash = spl_object_hash( $input );
if( !isset( $objInstances[ $class ] )){
$objInstances[ $class ] = array();
}
$output = 'object(%s) #%s (%s){%s}'; //class, instance, prop_count, props
if( false === ( $index = array_search($hash, $objInstances[ $class ] ) ) ){
$index = count($objInstances[ $class ]); //set init index for instance
$objInstances[ $class ][] = $hash;
// .... debugging code
$output = 'debugging result.', //sprintf
}else{
$output = sprintf( $output, $class, $index, 0, '#_CIRCULAR_REFRENCE_#');
}
Obviously the debugging code is way more complex, but the essential thing here is that by tracking the class and spl hash in $objInstances I can easily assign my own instance numbers outside of the class. This means I don't need some ugly hack ( that affects the class's code ) to get a reference number. Also, I don't need to display the "ugly" spl hash. Anyway my full code for this outputs something like this.
$obj = new TestObj();
$obj1 = new TestObj();
$obj->setProProp($obj1);
$obj1->setProProp($obj); //create a circular reference
object(TestObj) #0 (7){
["SOME_CONST":const] => string(10) 'some_const',
["SOMEOTHER_CONST":const] => string(16) 'some_other_const',
["SOME_STATIC":public static] => string(6) 'static',
["_PRO_STATIC":protected static] => string(10) 'pro_static',
["someProp":public] => string(8) 'someProp',
["_pro_prop":protected] => object(TestObj) #1 (7){
["SOME_CONST":const] => string(10) 'some_const',
["SOMEOTHER_CONST":const] => string(16) 'some_other_const',
["SOME_STATIC":public static] => string(6) 'static',
["_PRO_STATIC":protected static] => string(10) 'pro_static',
["someProp":public] => string(8) 'someProp',
["_pro_prop":protected] => object(TestObj) #0 (0){#_CIRCULAR_REFRENCE_#},
["_proProp":protected] => string(7) 'proProp'
},
["_proProp":protected] => string(7) 'proProp'
}
As you can see it's very easy to see where object(TestObj) #0 (0){#_CIRCULAR_REFRENCE_#} came from now. I wanted to keep this debugging code as close to the native var_dump
which outputs this.
object(TestObj)#7 (3) {
["someProp"]=> string(8) "someProp"
["_pro_prop":protected]=> object(TestObj)#10 (3) {
["someProp"]=> string(8) "someProp"
["_pro_prop":protected]=> *RECURSION*
["_proProp":protected]=> string(7) "proProp"
}
["_proProp":protected]=> string(7) "proProp"
}
The difference here is I needed the return as a string, not output to the browser. I also wanted to be able to show class constants, static properties, and private properties ( with flags to change what the debugger outputs, and the depth limit). And, I wanted a bit more information as to what the circular reference was instead of just *RECURSION* which doesn't tell me anything.
Hope it helps someone in the future.
Here is the full code for my Debug class, you can find this used about line #300
https://github.com/ArtisticPhoenix/Evo/blob/master/Evo/Debug.php
