Summary of Distinct Changes Required for PHP 7.4 Upgrade:
1. Deprecated split() function: This function is entirely removed in PHP 7.0
Change: Replace all instances of split() with preg_split()
2. Unparenthesized expressions with concatenation and arithmetic operators: Using a . (concatenation) before a + or - (arithmetic) without parentheses has been deprecated in PHP 7.4
Change: Add parentheses to explicitly define the order of operations in expressions containing both string concatenation (.) and arithmetic operations (+, -).
3. Parameter shadowing superglobals (e.g., $_POST): Defining a function parameter with the same name as a superglobal variable (like $_POST) causes a fatal error since PHP 5.4
Change: Rename the function parameters that shadow superglobal variables to avoid naming conflicts.
4. Multiple parameters with the same name in functions: PHP 7.0 and later forbid functions from having multiple parameters with identical names
Change: Ensure all function parameters have unique names.
5. break or continue with a 0 argument: Using 0 as an argument for break or continue is forbidden since PHP 5.4
Change: Remove the 0 argument from break or continue statements, as break; or continue; (without an argument) behaves as break 1; or continue 1;. If targeting a specific loop level, use a positive integer greater than 0
6. Deprecated INI directive mbstring.func_overload: This INI directive is deprecated since PHP 7.2
Change: Remove or update configurations related to mbstring.func_overload. This feature indicates that string functions should be overloaded with mbstring equivalents, which is generally not recommended in modern PHP.
7. Deprecated INI directive safe_mode: The safe_mode INI directive was deprecated in PHP 5.3 and removed in PHP 5.4
Change: Remove any references to safe_mode from your php.ini files or code that checks for it.
8. Deprecated get_magic_quotes_runtime() function: This function is deprecated since PHP 7.4
Change: Remove calls to get_magic_quotes_runtime(). magic_quotes_runtime was a security feature (or anti-feature, depending on perspective) that is no longer relevant.
9. Deprecated set_magic_quotes_runtime() function: This function was deprecated in PHP 5.3 and removed in PHP 7.0.
Change: Remove calls to set_magic_quotes_runtime().
10. Deprecated INI directive magic_quotes_runtime: This INI directive was deprecated in PHP 5.3 and removed in PHP 5.4.
Change: Remove any references to magic_quotes_runtime from your php.ini files or code.
11. Deprecated __autoload() function: The __autoload() function is deprecated since PHP 7.2
Change: Replace __autoload() with PSR-4 compliant autoloading using Composer, or a custom autoloader that utilizes spl_autoload_register().
12. Left-associativity of the ternary operator: The left-associativity of the ternary operator (?:) has been deprecated in PHP 7.4 when multiple consecutive ternaries are detected without explicit parentheses14.
Change: For nested ternary operations, use parentheses to explicitly define the order of evaluation to avoid ambiguity and ensure consistent behavior across PHP versions. Example: (expr1 ? expr2 : expr3) ? expr4 : expr5.