O que C# 4.0 não tem que C# 5.0 trouxe?

The C# language has evolved constantly to meet modern development needs, with versions 4.0 and 5.0 marking significant leaps in flexibility and modern asynchronous support. C# 4.0, released in 2010, focused on interoperability, particularly with COM libraries, and introduced features like dynamic typing, optional and named parameters, and co/contravariance. The dynamic keyword allows for dynamic typing with runtime resolution, ideal for interoperating with COM, JSON, or dynamic APIs. Optional and named parameters reduce the need for multiple overloads and make method calls more readable. Co/contravariance enables greater compatibility with related generic types. C# 5.0, released in 2012, introduced complete support for asynchronous programming based on tasks with the async and await keywords. This model replaced the callback and event pattern, making asynchronous programming much simpler and more readable. The async/await model allows for cleaner, more readable code, better performance in web apps, and avoids thread blocking. C# 4.0 is suitable for interoperating with Office, COM, or dynamic APIs, while C# 5.0 is ideal for applications heavily dependent on IO-bound asynchronous calls. Understanding these versions helps developers better comprehend the design of modern C# (8.0+).