Variables in PHP can be passed by value or by reference. It depends on the data type of the variable and how it is passed to a function.
Pass by value:
Simple data types:
Integers (int)
Floating-point numbers (float)
Strings (string)
Boolean values (bool)
Copies created:
When variables of these types are passed to a function, copies of their values are created.
Changes made to the copies inside the function do not affect the original variables.
Pass by reference:
Complex data types:
Arrays (array)
Objects (object)
Reference to the original:
When variables of these types are passed to a function, a reference to the original variable is passed, not a copy.
Changes made to the variable inside the function also change the value of the original variable.
How to determine how a variable is passed:
Ampersand symbol (&):
Before the variable name in the function parameter: pass by reference.
Example: function 'foo(&$bar) { ... }'
Absence of the & symbol:
Pass by value.
Example: function 'foo($bar) { ... }'
