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Q:

instantiate a class from a variable in PHP?

Hey everyone,

I'm fairly new to PHP and I'm currently working on a project where I need to instantiate a class, but the class I need to instantiate is stored in a variable. I've been searching online for possible solutions, but I haven't found anything that works for me yet.

Here's the situation: I have a form where users can select a specific class from a dropdown menu. The selected class is then stored in a variable $className. Now, I want to be able to create an instance of the selected class, but I'm not sure how to do that since the class name is stored in a variable.

I've tried using the "new" keyword like this:

$instance = new $className();

But this doesn't seem to work. I keep getting a syntax error. I've also tried using the class_exists() function to check if the selected class exists before trying to instantiate it, but that doesn't work either.

I would really appreciate it if someone could point me in the right direction. Is there a way to dynamically instantiate a class using a variable in PHP? What am I missing here?

Thanks in advance!

All Replies

walter.angel

Hey,

I've come across a similar situation in my PHP projects where I needed to instantiate a class using a variable. The "new" keyword can indeed be used, as you mentioned, to dynamically create an instance of a class based on a variable.

However, the syntax error you mentioned could be due to incorrect usage or a compatibility issue. One thing you can try is using the variable within curly braces, like so:

php
$instance = new {$className}();


By enclosing the variable name in curly braces, it helps resolve any ambiguity and allows proper instantiation of the class.

Alternatively, you might want to verify if there are any namespaces involved. If your class belongs to a namespace, you need to include it during instantiation:

php
$instance = new \Namespace\{$className}();


Remember to replace `\Namespace\` with the actual namespace your class belongs to.

If you still encounter errors, double-check that the variable $className holds the right class name and that the corresponding class is correctly defined in your code.

Hopefully, these suggestions help you resolve the syntax error and instantiate the necessary class dynamically. Feel free to ask if you need further assistance!

darrion.marks

Hey there,

Yes, you can definitely instantiate a class using a variable in PHP. I have encountered this situation before and managed to solve it. The syntax error you are experiencing might be due to some small mistake in your code.

To dynamically instantiate a class using a variable in PHP, you can use the following code:


$instance = new $className;


Make sure that the value of $className is a valid class name and that the corresponding class is properly defined and accessible in your code. Note that the parentheses after $className are optional if you don't have any constructor arguments.

Also, if you are unsure whether the selected class exists, it's a good practice to check it using the class_exists() function before instantiating. Here's an example:


if (class_exists($className)) {
$instance = new $className;
} else {
// Handle the case where the selected class doesn't exist
}


By incorporating this conditional check, you can ensure that your code won't throw any errors when trying to instantiate a non-existent class.

I hope this helps! Let me know if you have any further questions.

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