In Magento 2, one of the new properties is Magento 2 Virtual Type. What are they for?

Imagine that you already have a class A available:

namespace VendorName\ModuleName\Model
class A
{
    protected $arg1;
    protected $arg2;
    protected $arg3;

    public function __construct(
        Argument1 $arg1,
        Argument2 $arg2,
        Argument3 $arg3
    ) {
        $this->arg1 = $arg1;
        $this->arg2 = $arg2;
        $this->arg3 = $arg3;
     }
}

And you need to create a class B, which will be inherited from A. However, it must take another argument as $arg2. To do this, you will create a new PHP file for class B:

namespace Me\MyModule\Model
class B extends A
{
    public function __construct(
        Argument1 $arg1,
        SomeOtherArg $someOtherArg,
        Argument2 $arg3
    ) {
parent::__construct($arg1, $someOtherArg, $arg3)
     } }

But you don't need to do this in Magento 2. In such cases, virtual types are created. Therefore, create the etc/di.xml file in  your module folder and add the following code to it:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <virtualType name="Me\MyModule\Model\B" type="VendorName\ModuleName\Model\A">
        <arguments>
            <argument name="arg2" xsi:type="string">SomeOtherArg</argument>
        </arguments>
     </virtualType>
</config>

Regenerate DI using the command::

php bin/magento setup:di:compile

Now your can use the Me\MyModule\Model\B

You can read more about the virtual types on Alan Storm Blog.