Force what is being given as a string parameter in php - php

Question

I've searched for the answer to my problem, but I'm having trouble putting it to words. So... I'm asking here.
I have a method which is created to echo text with a given string and an error type:
public function output($string, $errorType) : void
{
echo "<div class='alert alert-$errorType' role='alert'>$string</div>";
}
Since I'm using bootstrap, this $errorType should always be warning, danger or success. But since it's a string, I can give $errorType an entirely different value. I want to force the usage of the three error types: warning, danger or success. What is the best way to do this?

Answer 1

This question is one of input validation.
In your context, there's several approaches you can take. The ultimate goal is to check if the input is in a list of accepted values, but the main question is where, when and how to do this.
The most intuitive approach would be to put it right inside the method, eg
if (!in_array($input, self::ACCEPTABLE_INPUT)) {
throw some exception
}
An alternative mechanism in the same spirit would be to use assert:
assert(in_array($input, self::ACCEPTABLE_INPUT));
However this assumes a decent test coverage.
One way which I generally tend to prefer is to model the error type as a value object, eg.
final class ErrorType
{
private const ACCEPTED = ['warning', 'danger', 'success'];
private $type;
public function __construct(string $type)
{
if (!in_array($type, ErrorType::ACCEPTED) {
throw some exception
}
$this->type = $type;
}
public function __toString(): string
{
return $this->type;
}
}
It's a bit more code, but allows you to follow the Single Responsibility Principle.
Your function would simply look like this:
public function output($string, ErrorType $errorType) : void
{
echo "<div class='alert alert-$errorType' role='alert'>$string</div>";
}

Answer 2

Throw an Exception if input value of $errorType is not a valid value. You can do something like as below:
public function output($string, $errorType) : void
{
// define all possible valid input values for $errorType
$accepted_error_type = array('warning', 'danger', 'success');
// throw exception if invalid input
if (!in_array($errorType, $accepted_error_type) {
throw new Exception('Invalid errorType in function output. Expected: warning, danger or success. Received: ' . $errorType);
}
// Rest of the implementation details come here
echo "<div class='alert alert-$errorType' role='alert'>$string</div>";
}

Answer 3

You can let users to give int as $errorType. For example 0 for warning, 1 for danger, 2 for success. For other values, you can either set a default value (for example warning) or you can return exception.
public function output($string, $errorType)
{
$type = "";
if($errorType == 0)
$type = "warning";
else if($errorType == 1)
$type = "danger";
else if($errorType == 2)
$type = "success";
else
{
// You can set a default error type here, if input is incorrect
// Or you can simply return an exception to inform user about limitations.
}
echo "<div class='alert alert-$type' role='alert'>$string</div>";
}