question regarding classes namespace

thehedgehog

i'm wondering if this is generally a bad idea...

<?
class test {
var $var1;
var $var2;

function Set($varname,$value) {
          $this->$varname=$value;
     }

}

$fanks = new test;
$fanks->Set('var1','foo');
$fanks->Set('var2','bar');

$fanks = new test;
$fanks->Set('var1','hello world');


echo "{$fanks->var1} {$fanks->var2}";
?>

it seems once i create the second instance, the namespace is totally wiped - ie: this will only print "hello world", rather than "hello world bar".

i guess i'm a bit curious as to what's actually going on here. is the original object simply destroyed and replaced with this?
of course i don't need to have a same-named instance, that's not a big deal, but i'm wondering if there's an equivalent of class_exists() for instances. object_exists(), or something of that nature.

mainly i just would rather not have a billion objects all holding variables if i can append to (or reset) objects. often i'm creating new objects inside a function, and tracking if i've already opened the object in a previous function is a lot of architectural flow work i'd like to avoid if possible. 😛

(i suppose i should nest more of the functions into the classes they address and make better use of $this->var, etcetera.)

a $connection->queryString() function is a prime example, since i can reuse the same object namespace and just forget about it.

then again i dunno, i'm an intermediate level developer at best and probably going down the same OOP pitfall that most people in my learning level do, namely using classes largely for a big treasure trunk of vars and functions... is it that horrible to have a dozen instances all open at once?

drew010

the reason the data goes away is because the new operator, creates a new instance of a class and assigns it to the variable on the left of the = sign. since it is being created new, it overwrites the old instance of the class, thus destroying the contents of var2. you may have the wrong understanding of namespaces. php doesnt really have namespaces. you can create a second instance of the class using a different variable name and the contents of the first instantiation will still be available.

thehedgehog

right, yeah i'm understood on the idea that i can just use different object names in order to not reset all the variables in a class, i guess what i'm wondering is if there's a way to check if there's an instance of that class already available.

i think probably my problem is that i've got a class with far too many variables (my primary class has about 34 - it's a fairly involved cms, heh.)

since most of the functions set some of the class variables within an object, i'd rather utilize those rather than getting them again in a seperate function if they're already set (some of the information the functions pull down has to overlap a bit for them to be repurposeable.)

so i guess my primary concern is:

a] is there a way to determine if an instance exists that has a value for a given variable in a given class.

b] is it really all that bad if i just create half a dozen instances rather than dealing with a].

yeah, i've always heard of namespace referring to the freeing up of variables within a function (php keeps variable names within the function unless you declare them as global, to free up namespace i think was one thing i heard that might have confused me on this), so i've probably completely missed the point of what that's actually supposed to be referring to.

frankly i'm still surprised i figured out what a variable is used for :]

drew010

for question a you only need to use a simple if statement.

if ($obj->var == "something") { //check instance

and for b, yes usually unless the different objects are being used for totally different purposes you should use as few of the objects as possible. you can think of it on a smaller scale as having 7 different variables holding the same information and depending on where you are in the script you pick a different variable. in that case you really only need one and having more is a waste of memory and makes the code harder to follow and understand.