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PHP: Exceptions, Errors and Throwable

Before PHP 7, error handling and exception handling were quite distinct:

  1. Exceptions (Exception Class): Exceptions were used for handling exceptional conditions in the application flow. They could be caught using try-catch blocks. Exceptions are part of PHP’s object-oriented programming features.
  2. Errors: Errors were traditionally handled separately from exceptions. They represented issues in the PHP script, like syntax errors, missing files, or undefined variables. Errors were typically managed using functions like set_error_handler() rather than try-catch blocks.

PHP 7 and Later: Introduction of Throwable

With PHP 7, the error handling model was significantly reformed:

  • Throwable Interface: PHP 7 introduced a new base interface called Throwable. Both Exception and a new class called Error implement this interface.
  • Error Class: The Error class is similar to Exception, but it is used for errors that occur at the PHP engine level. These include things like type errors, argument count errors, and more.
  • Catching Errors and Exceptions: With the introduction of Throwable, PHP allowed both errors and exceptions to be caught in the same way. This means that you can catch Error, Exception, and their subclasses by catching Throwable.

Example of Using Throwable

try {
    // Code that may throw an Exception or raise an Error
} catch (Throwable $t) {
    // Handle both Exception and Error objects
}
  • Backward Compatibility: Existing exception handling code (catching Exception) continues to work as before. However, it won’t catch errors of the Error class.
  • Error Severity: Not all errors are converted to Error objects. Traditional error handling still applies to warnings, notices, etc.
  • Best Practices:
    • Use Throwable to catch both Error and Exception when you want a broad safety net.
    • Be cautious when catching Error. Some errors indicate critical problems in your code (like calling a method on null) that should ideally be fixed rather than caught and ignored.
    • Ensure adequate logging and reporting when catching Throwable to diagnose and address underlying issues.

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