ArgumentCountError — Wrong Arg Count

TL;DR

Explanation

ArgumentCountError extends TypeError extends Error. It's thrown when a function requiring N parameters receives fewer. Too many arguments is only an error in strict mode or with variadic functions. Common scenarios: refactoring a function to require more parameters breaks all callers, calling a method with wrong interface signature. In PHP 8, named arguments allow skipping positional requirements but still enforce parameter count. Check with func_num_args() in legacy variadic code.

Common Misconception

Why It Matters

Common Mistakes

• Adding a required parameter to an existing function without updating all callers.
• Not using default values for new optional parameters.
• Calling parent::__construct() with wrong argument count in subclasses.

Code Examples

function createUser(string $name, string $email, string $role): User {
    // ...
}
createUser('Paul', 'paul@example.com');
// ArgumentCountError: Too few arguments (2), 3 required

// Add with a default value to avoid breaking callers:
function createUser(string $name, string $email, string $role = 'user'): User {
    // ...
}
// Or use named arguments (PHP 8):
createUser(name: 'Paul', email: 'paul@example.com', role: 'admin');

References

• ↗ https://www.php.net/manual/en/class.argumentcounterror.php

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