Type hints and automatic type conversion for PHP functions

PHP type hints declare the expected parameters and return types of functions to avoid type errors. It also provides automatic type conversion, throwing a type error when the conversion fails. These features enhance code readability, reduce errors, and improve compiler error detection, as shown in the example of validating a credit card number.

Type hints and automatic type conversion of PHP functions

Type hints

PHP 7 introduced type hints, allowing developers to declare the expected parameter types and return types of functions. This helps avoid type errors and improves code readability. For example:

function sum(int $a, int $b): int
{
    return $a + $b;
}

The above code declares that the sum() function receives two integer parameters and returns an integer value.

Automatic Type Conversion

PHP will usually try to automatically convert variables to the type expected by the function. If the conversion fails, a type error is thrown. For example:

sum(1, '2'); // 自动将 '2' 转换为整型 2
sum('1', 2); // 抛出类型错误，因为 '1' 不能转换为整型

Practical case

The following is a function that verifies whether a credit card number is valid:

function isValidCreditCard(string $cardNumber): bool
{
    // 验证卡号是否是 16 位数字
    if (!preg_match('/^\d{16}$/', $cardNumber)) {
        return false;
    }

    // 使用 Luhn 算法验证卡号
    $sum = 0;
    for ($i = 0; $i < strlen($cardNumber); $i++) {
        $digit = (int) $cardNumber[$i];
        if ($i % 2 === 0) {
            $digit *= 2;
        }
        $sum += $digit % 10 + ($digit / 10);
    }

    return $sum % 10 === 0;
}

Advantages

Type hints and automatic type conversion provide the following benefits:

• Reduce type errors
• Improve code readability and maintainability
• Enhancement Compiler’s ability to detect errors

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