silverstripe-framework/forms/FormTransformation.php

<?php
/**
 * This class represents "transformations" of a form - such as making it printable or making it readonly.
 * The idea is that sometimes you will want to make your own such transformations, and you shouldn't have
 * to edit the underlying code to support this.
 *
 * The first step in creating a transformation is subclassing FormTransformation.  After that, you have two
 * ways of defining specific functionality:
 *   - Define performMyTransformation() methods on each applicable FormField() object.
 *   - Define transformFieldType($field) methods on your subclass of FormTransformation.
 *
 * To actually perform the transformation, call $form->transform(new MyTransformation());
 * @package forms
 * @subpackage transformations
 */
class FormTransformation extends Object {
	public function transform(FormField $field) {
		// Look for a performXXTransformation() method on the field itself.
		// performReadonlyTransformation() is a pretty commonly applied method.
		// Otherwise, look for a transformXXXField() method on this object.
		// This is more commonly done in custom transformations

		// We iterate through each array simultaneously, looking at [0] of both, then [1] of both.
		// This provides a more natural failover scheme.

		$transNames = array_reverse(array_values(ClassInfo::ancestry($this->class)));
		$fieldClasses = array_reverse(array_values(ClassInfo::ancestry($field->class)));

		$len = max(sizeof($transNames), sizeof($fieldClasses));
		for($i=0;$i<$len;$i++) {
			// This is lets fieldClasses be longer than transNames
			if($transName = $transNames[$i]) {
				if($field->hasMethod('perform' . $transName)) {
					$funcName = 'perform' . $transName;
					//echo "<li>$field->class used $funcName";
					return $field->$funcName($this);
				}
			}

			// And this one does the reverse.
			if($fieldClass = $fieldClasses[$i]) {
				if($this->hasMethod('transform' . $fieldClass)) {
					$funcName = 'transform' . $fieldClass;
					//echo "<li>$field->class used $funcName";
					return $this->$funcName($field);
				}
			}
		}

		user_error("FormTransformation:: Can't perform '$this->class' on '$field->class'", E_USER_ERROR);
	}
}