PHP Objects and Variable Properties Question...

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Everett Reply #1, 17 years, 3 months ago

Well, this is strictly a PHP question, but I know you guys are smart and friendly, so I’m hoping someone can explain this to me.

I’m trying to store some data in a variable location in an object, and that data is various hash keys.

Consider the following code contained in one of my object’s functions:

$storage_loc = 'somewhere';

//  $this->$storage_loc[$key] = $value;  // don't work
//  $this->$storage_loc->$key = $value;  // works, but stores as an object
//  $this->$storage_loc = array_merge( $this->$storage_loc, array($key => $value) );  // Doesn't work
  $this->vars[$key] = $value;		   // static properties work fine

Why can’t I use a variable to identify an object PROPERTY? I can use a variable to define an object FUNCTION without any problems.

Thanks for any tips.

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kongondo Reply #2, 17 years, 3 months ago

Sorry to to ask a question of my own using your thread Everett. I have just resumed learning PHP (almost a total noob) and I am wondering whether

$this->$storage_loc[$key] = $value;

is correct syntax? My reading tells me that the -> symbol is used to connect objects to their properties or methods, and that the $ symbol is omitted before the variable/property name when accessing properties of a class instance. So, should be

$this->storage_loc[$key] = $value;

is that correct? Many thanks.

Like I said, I have only just started so feel free to ignore me since I probably don’t know what am talking about wink

cheers/k

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BobRay Reply #3, 17 years, 3 months ago

I not sure exactly what you’re trying to do, but I think this might be what you want (and Kongondo is correct about the extra dollar sign):

$storage_loc = array();

$this->storage_loc[$key] = $value;

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Chuck Reply #4, 17 years, 3 months ago

Sounds like you want to use traditional set and get methods (functions) to use a object (class) as a Data Transfer Object or what used to be call a Value Object.

// ==================================================
// START function

function setName($name) {

    $this -> name = $name;

} // END function
// ==================================================

// ==================================================
// START function

function getName() {

    return $this -> name;

} // END function
// ==================================================

This type of code is commonly used in conjunction with Data Access Objects.

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Everett Reply #5, 17 years, 3 months ago

No no, I am trying to set variable properties, so the syntax really is $this->$x

This works fine for a regular scalar variable. E.g. I can iterate over an array( ’a’,’b’,’c’) then perform a function on those, e.g.
$this->$x = $_POST[$x];

But what doesn’t work is storing the hashes. At least not directly. You can do something like $this->$x = array($param => $result);

This is different than the more common static methods (i.e. $this->x = array($param => $result); )

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sottwell Reply #6, 17 years, 3 months ago

So this is related to "variable variables", which is something that always fascinated me, but I never really did get my head wrapped around.
http://us2.php.net/manual/en/language.variables.variable.php

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Chuck Reply #7, 17 years, 3 months ago

Sorry for the misunderstanding. I wonder if this a job for enclosing the variable in question with curly brackets?

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BobRay Reply #8, 17 years, 3 months ago

Sorry, I thought you were attempting something simpler. I’ve never found a need for that form (always found a way to use straight associative arrays) and I’ve suspected that it would make my code harder to maintain and debug so, like Susan, I’m not much help on this one. I suspect that Chunk is correct about the curly braces.

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Everett Reply #9, 17 years, 3 months ago

Yeah, I tried the variable variables syntax, but couldn’t get it to work. Ultimately, I solved the issue in another way that cleaned up my code

I guess the lesson is that if it takes too long to come up with some crazy syntax, then maybe there’s an easier way...

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kongondo Reply #10, 17 years, 3 months ago

...And I have learned something new...

cheers/k

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