Exception Hierarchy (Throwable, Error, Exception)

TL;DR

Explanation

PHP 7 introduced Throwable as the root interface. Exception (user exceptions) and Error (engine errors like TypeError, ParseError, ArithmeticError) both implement it. Before PHP 7, fatal errors like calling undefined functions were uncatchable. Now: catch (\Throwable $t) catches everything. catch (\Error $e) catches engine errors. catch (\Exception $e) catches application exceptions. Key subclasses: TypeError (wrong types), ValueError (invalid argument values), ArithmeticError / DivisionByZeroError, ParseError, Error.

Common Misconception

Why It Matters

Common Mistakes

• Catching Exception when Error subclasses are possible — use Throwable.
• Not distinguishing between recoverable errors (TypeError from user input) and programming errors (wrong arg type in internal code).
• Swallowing Throwable in catch blocks without logging.

Code Examples

try {
    $result = intdiv($a, 0);
} catch (Exception $e) {
    // Misses DivisionByZeroError — it's an Error, not Exception
    echo "caught";
}

try {
    $result = intdiv($a, 0);
} catch (DivisionByZeroError $e) {
    $result = 0; // specific handling
} catch (\TypeError $e) {
    throw new InvalidArgumentException('Numeric values required', 0, $e);
} catch (\Throwable $t) {
    // Last resort — log everything
    logger()->critical('Unhandled', ['exception' => $t]);
    throw $t;
}

References

• ↗ https://www.php.net/manual/en/language.exceptions.php

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