Adapters

Easy.php

<?php
interface FilterAdapter
{
    public function filter($value);
}

class FilterBase
{
    protected $_adapter;

    public function getAdapter()
    {
        return $this->_adapter;
    }

    public function setAdapter(FilterAdapter $filter)
    {
        $this->_adapter = $filter;
        return $this;
    }

    public function filter($value)
    {
        return $this->getAdapter()->filter($value);
    }
}

//Old filter adapter
class FilterArrayAdapterHard implements FilterAdapter
{
    public function filter($value)
    {
        if (!is_array($value)) {
            throw new InvalidArgumentException('$value should be an array.');
        }
        $tmp = array();
        foreach ($value as $k => $v) {
            if (!empty($v)) {
                $tmp[$k] = $v;
            }
        }
        return $tmp;
    }
}

//New filter adapter
class FilterArrayAdapterEasy implements FilterAdapter
{
    public function filter($value)
    {
        if (!is_array($value)) {
            throw new InvalidArgumentException('$value should be an array.');
        }
        return array_filter($value);
    }
}

$foo = array('foo', 'bar', 0);
$filter = new FilterBase();
var_dump($filter->setAdapter(new FilterArrayAdapterEasy())->filter($foo));

Hard.php

<?php
interface FilterAdapter
{
    public function filter($value);
}

class FilterBase
{
    protected $_adapter;

    public function getAdapter()
    {
        return $this->_adapter;
    }

    public function setAdapter(FilterAdapter $filter)
    {
        $this->_adapter = $filter;
        return $this;
    }

    public function filter($value)
    {
        return $this->getAdapter()->filter($value);
    }
}

class FilterArrayAdapterHard implements FilterAdapter
{
    public function filter($value)
    {
        if (!is_array($value)) {
            throw new InvalidArgumentException('$value should be an array.');
        }
        $tmp = array();
        foreach ($value as $k => $v) {
            if (!empty($v)) {
                $tmp[$k] = $v;
            }
        }
        return $tmp;
    }
}

$foo = array('foo', 'bar', 0);
$filter = new FilterBase();
var_dump($filter->setAdapter(new FilterArrayAdapterHard())->filter($foo));