What are some common PHP version discrepancies that may affect code functionality, such as automatic concatenation operators?

One common PHP version discrepancy that may affect code functionality is the use of automatic concatenation operators. In older versions of PHP (5.x), the automatic concatenation operator (.) was used to concatenate strings, while in newer versions (7.x), the concatenation assignment operator (.=) is preferred for better performance. To ensure code compatibility across different PHP versions, it is recommended to use the concatenation assignment operator (.=) instead of the automatic concatenation operator (.).

// Using concatenation assignment operator (.=) for better performance and compatibility
$string1 = "Hello";
$string2 = "World";
$string1 .= $string2;
echo $string1; // Output: HelloWorld