What is the Use of Type and Virtual Types(di.xml) in Magento2?

Question

I want to know clear about Type and Virtual Types in di.xml with examples. When we can use it.

Please share simple example to understand concept.

Note please go through the practical examples.

Answer 1

Virtual types are a way to inject different dependencies into existing classes without affecting other classes.

For Example, the Magento\Framework\Session\Storage class takes a $namespace argument in its constructor, which defaults to the value default, and you could use the type definition to change the namespace to core.

<type name="Magento\Framework\Session\Storage">
    <arguments>
        <argument name="namespace" xsi:type="string">core</argument>
    </arguments>
</type>

The above config would make it so that all instances of Magento\Framework\Session\Storage have a namespace of core. Using a virtual type allows for the equivalent of a sub-class to be created, where only the sub-class has the altered argument values.

In the codebase we see the following two configurations:

<virtualType name="Magento\Core\Model\Session\Storage" type="Magento\Framework\Session\Storage">
    <arguments>
        <argument name="namespace" xsi:type="string">core</argument>
    </arguments>
</virtualType>

<type name="Magento\Framework\Session\Generic">
    <arguments>
        <argument name="storage" xsi:type="object">Magento\Core\Model\Session\Storage</argument>
    </arguments>
</type>

The first snippet creates a virtual type for Magento\Core\Model\Session\Storage which alters the namespace, and the second inject the virtual type into Magento\Framework\Session\Generic. This allows Magento\Framework\Session\Generic to be customized without affecting other classes that also declare a dependency on Magento\Framework\Session\Storage