Functions · Lesson 5 of 9
Default Parameters
Provide optional values with defaults at the end of a parameter list.
Lesson
A default parameter lets callers omit an optional argument. Required parameters should come before optional ones, and defaults should be simple, predictable values. Avoid a default that disguises a missing required business decision; validate important choices explicitly.
Callers can use the default or override it when a different value is appropriate.
Further guidance
Treat a function as a small contract: name its inputs, state what it returns, and avoid hidden dependencies. Test a representative value and an edge case. Keep a function focused; callers should decide how to display a returned result or handle a reported failure.
Practice task: Create a fresh example for Default Parameters. Predict the result before running it, then change one input and explain why the result changes. Test a normal case and one boundary or invalid case where it applies. Compare your output with the example and note one rule you would use in a real project.
Code examples
Default Parameters
PHP
function greet(string $name, string $salutation = 'Hello'): string
{
return "$salutation, $name";
}
echo greet('Sam');Expected output
Hello, Sam
Key points
- Provide optional values with defaults at the end of a parameter list.
- Keep inputs, return values, and side effects explicit.
- Prefer focused functions that are easy to test independently.
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