A virtual type is a dependency injection (DI) configuration that defines a subclass in di.xml without requiring a physical PHP class file. Its primary purpose is to change the constructor arguments for an existing class for a specific injection context. In this scenario, a global preference could conflict with the legacy extension. A virtual type allows the developer to create a specific configuration of a core class (e.g., a service in the checkout process) and inject their new custom tax calculator into it. This targets the change precisely to the checkout process, avoiding global modifications and ensuring the new logic coexists with core and legacy calculations without altering their code.

A. Constructor arguments: This is a general DI feature for defining a class's dependencies, not the specific mechanism for substituting one implementation for another in a targeted way, which is required here.

C. Preferences: A preference creates a global override for a class or interface. This is too broad and would likely conflict with the existing legacy extension or have unintended side effects in other areas.

1. Adobe Commerce Developer Guide

"Virtual types": "Use a virtual type to change the arguments of a specific class dependency. This is useful when you want to inject a different version of a class into a specific object

without affecting other objects that use the same class." This directly supports using a virtual type for a targeted change

as required by the scenario.

Source: Adobe Commerce Developer Documentation

Fundamentals > Dependency injection > Virtual types.

2. Adobe Commerce Developer Guide

"Preferences": "A preference is a global override. When you declare a preference

it affects all instantiations of that class." This explains why a preference is unsuitable for this scenario

as a global change could break the legacy extension's functionality.

Source: Adobe Commerce Developer Documentation

Fundamentals > Dependency injection > Preferences.

3. Adobe Commerce Developer Guide

"Object management": The documentation on DI illustrates that while constructor arguments are fundamental

mechanisms like virtual types and plugins are provided for more complex customization scenarios

such as altering dependencies for specific consumers without modifying their code.

Source: Adobe Commerce Developer Documentation

Fundamentals > Architectural layers > Object management.