I'm learning php and I ran into the following head-scratcher:
I have 2 objects, let's say
class Fruit {
public $weight;
}
$apple = new Fruit();
$apple->weight = 1;
$banana = new Fruit();
$banana->weight = 2;
Later on, from I get some input from the user as a variable (like, which fruit do you like best?):
$user_preference = 'apple';
Now, how can I reference the correct object dynamically? How to get something like
echo $user_preference->weight;
?
I would create a map (usefull when data is retrieved from a db for example)
$apple = new Fruit();
$apple->weight = 1;
$banana = new Fruit();
$banana->weight = 2;
$fruitMap = ['apple'=>$apple,'banana'=>$banana];
$user_preference = 'apple';
echo $fruitMap[$user_preference]->weight;
But do a check if the key exists
You can use Variable variables :
<?php
class Fruit {
public $weight;
}
$apple = new Fruit();
$apple->weight = 1;
$banana = new Fruit();
$banana->weight = 2;
$user_preference = 'apple';
// vv---------------- Check this notation
echo $$user_preference->weight; // outputs 1
Note that this can lead to security breaches because
Imagine you do echo $$user_input; and user input is database_password
To avoid it, you need to sanitize user inputs, in example :
<?php
class Fruit {
public $weight;
}
$apple = new Fruit();
$apple->weight = 1;
$banana = new Fruit();
$banana->weight = 2;
$allowed_inputs = ['apple', 'banana'];
$user_preference = 'apple';
if (in_array($user_preference, $allowed_inputs))
{
echo $$user_preference->weight; // outputs 1
}
else
{
echo "Nope ! You can't do that";
}
But this is at the cost of typing more code. ka_lin's solution is safer and easier to maintain
echo $$user_input; and user input is database_password
echo ${$user_preference}->weight;orecho $$user_preference->weight;. See variable variables. It's not exactly a recommended feature to use in most cases though.