Using braces with dynamic variable names in PHP

I'm trying to use dynamic variable names (I'm not sure what they're actually called) But pretty much like this:

for($i=0; $i<=2; $i++) {
    $("file" . $i) = file($filelist[$i]);
}

var_dump($file0);

The return is null which tells me it's not working. I have no idea what the syntax or the technique I'm looking for is here, which makes it hard to research. $filelist is defined earlier on.

Solution 1:

Wrap them in {}:

${"file" . $i} = file($filelist[$i]);

Working Example

Using ${} is a way to create dynamic variables, simple example:

${'a' . 'b'} = 'hello there';
echo $ab; // hello there

Solution 2:

Overview

In PHP, you can just put an extra $ in front of a variable to make it a dynamic variable :

$$variableName = $value;

While I wouldn't recommend it, you could even chain this behavior :

$$$$$$$$DoNotTryThisAtHomeKids = $value;

You can but are not forced to put $variableName between {} :

${$variableName} = $value;

Using {} is only mandatory when the name of your variable is itself a composition of multiple values, like this :

${$variableNamePart1 . $variableNamePart2} = $value;

It is nevertheless recommended to always use {}, because it's more readable.

Differences between PHP5 and PHP7

Another reason to always use {}, is that PHP5 and PHP7 have a slightly different way of dealing with dynamic variables, which results in a different outcome in some cases.

In PHP7, dynamic variables, properties, and methods will now be evaluated strictly in left-to-right order, as opposed to the mix of special cases in PHP5. The examples below show how the order of evaluation has changed.

Case 1 : $$foo['bar']['baz']

• PHP5 interpetation : ${$foo['bar']['baz']}
• PHP7 interpetation : ${$foo}['bar']['baz']

Case 2 : $foo->$bar['baz']

• PHP5 interpetation : $foo->{$bar['baz']}
• PHP7 interpetation : $foo->{$bar}['baz']

Case 3 : $foo->$bar['baz']()

• PHP5 interpetation : $foo->{$bar['baz']}()
• PHP7 interpetation : $foo->{$bar}['baz']()

Case 4 : Foo::$bar['baz']()

• PHP5 interpetation : Foo::{$bar['baz']}()
• PHP7 interpetation : Foo::{$bar}['baz']()