On August 19, Microsoft announced the fourth generation of its Proxy library, a C++20 toolkit designed to simplify polymorphic programming. Available as an open-source project on GitHub, Proxy 4 provides developers with lightweight abstractions that eliminate much of the boilerplate associated with inheritance and virtual functions.

What the Library Offers

The updated release focuses on runtime polymorphism while remaining header-only and cross-platform. Key additions include:

• Re-usable facade components that allow developers to assemble higher-level interfaces more flexibly.
• New alias types—proxy_view and weak_proxy—that simplify expressing borrowing semantics and weak ownership in modern C++.
• Shared and weak proxy utilities, such as make_proxy_shared and allocate_proxy_shared, which aim to deliver the functionality of std::shared_ptr with less overhead and more efficient memory usage.
• Support for recursive operator patterns via facade_aware_overload_t, enabling operations like chaining arithmetic or concatenation without premature instantiation of proxy objects.

Practical Use Cases

The new aliases play an important role in day-to-day coding. For instance, proxy_view lets a developer access an object without taking ownership of it, while weak_proxy creates a reference that can later be locked if needed. This helps coders manage lifetimes safely without incurring unnecessary resource costs.

Tools for Developers

To showcase Proxy 4 and encourage experimentation, Microsoft also unveiled an integrated online playground through Compiler Explorer. The tool allows developers to write, run, and test Proxy code directly in their browser, lowering the barrier for adoption and learning.

Why It Matters

With Proxy 4, Microsoft is positioning the library as a modern alternative to classical inheritance hierarchies, helping developers achieve polymorphism in a way that is cleaner, safer, and more performance-conscious.