What are the rules for the return value of a custom PHP function?

Return value rules for custom PHP functions: All functions must return a value (can be NULL). Use the return keyword or implicitly return the last expression value. The return value must be the value itself, not a reference.

The return value of a custom PHP function: rules and practice

In PHP, the return value of a custom function follows certain rules Rules to ensure code maintainability and predictability.

Rules:

• All functions must return a value, and the type can be any valid data type (including NULL).
• If a function does not explicitly return a value, it will return NULL by default.
• You can use the return keyword to return a value, or you can have the function implicitly return the value of the last expression.
• The return value cannot be a reference, it must be the value itself.

Practical case:

Create a custom function calculateSum(), which calculates the sum of two numbers:

<?php
function calculateSum($num1, $num2) {
    $sum = $num1 + $num2;
    return $sum; // 显式地返回和
}

// 使用函数
$result = calculateSum(5, 10);
echo "The sum is: $result"; // 输出 15
?>

In this example, the function calculateSum() returns the calculated sum of type int. It uses the return keyword to explicitly specify the return value.

Note:

• Ensure that the function correctly handles all possible input scenarios, including invalid inputs and boundary conditions.
• Clearly specify return value types in documentation to improve code readability and maintainability.
• Following these rules is critical to writing clean, reusable, and maintainable PHP functions.

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