Flute's fluent interface is heavily inspired by FluentValidation for .NET.

Here is a simple example to get you started :

require 'path/to/flute.php';

$validator = new Validator();
$validator->rule_for('first_name')->max_length(100);

$p = new Person('John');
$result = $validator->validate($p);

if ($result->valid()) {
	echo 'Valid!';
}

These validation rules are supported out of the box :

• NotNull
• NotEmpty
• Required
• MaxLength
• ... (and many more. You can also add rules yourself)

It's very easy to create custom rules, and you don't even have to alter the Validator class. Everything is done with magic naming conventions! For example, here is how the NotEmpty rule is built :

// The naming is very important here. More on that later.
class NotEmptyRule extends Rule // We must extend the Rule abstract class
{
	//We override the condition function to run our own validation logic
	public function condition($value)
	{
		// The $value variable contains the value we need to validate.
		// For this particular case, it is considered valid if it is
		// not equal to the empty string.
		return $value !== '';
	}
}

Once your rule is defined, it must be discoverable by any registered auto-loader in order the make it available to the Validator class. Here is how you invoke it :

// Create an instance of the validator
$v = new Validator();

$v->rule_for('first_name')->not_empty();

See what I did there? No need to add the not_empty() function to the validator. Any unknown function invoked on a validator will create a rule named with the following conventions :

• Every word delimited by underscores is capitalized.
• The underscores are removed.
• 'Rule' is appended to the resulting string.

So not_empty becomes NotEmptyRule. The validator will instantiate a NotEmptyRule class and associate it with the property name defined when we called rule_for. Easy, huh?

Very simple. Here is a brief look at the MaxLengthRule implementation.

class MaxLengthRule extends Rule
{
	public function condition($value)
	{
		return strlen($value) <= $this->max_length;
		//W-w-w-wait, what!? Where does max_length come from?
	}
}

$v = new Validator();
$v->rule_for('first_name')->max_length(100);

Any parameters passed to the function definition will be registered in the args array in the same order that they were passed to the validator rule. You can also access args with the magic __get method, like I did here with max_length. I you were to call max_length again, it will send back the same value as the first time it was called. When using multiple arguments, they are handed out in the order they were passed, and each name gets its own argument.

Your custom rule can extend the behaviour of existing rules. Let's take a look at the RequiredRule implementation :

class RequiredRule extends Rule
{
	public function extend() {
		return array(
			new NotNullRule(),
			new NotEmptyRule()
		);
	}
}

As you can see, the RequiredRule is only a combination of the NotNullRule and the NotEmptyRule. The extend function returns an array of instantiated rules which you want to extend. The condition function will be called on both rules and combined with a logical and. That is, if any of the condition fails, it is considered invalid.

That's it for the moment! Stay tuned for more awesome features!