Plurrrr

One of the things that makes DNS difficult to understand is that it’s decentralized. There are thousands (maybe hundreds of thousands? I don’t know!) of authoritative nameservers, and at least 10 million resolvers. And they’re running lots of different software! All these different servers running software means that there’s a lot of inconsistency in how DNS works, which can cause all kinds of frustrating problems.

When faced with a situation where you're writing code that should work across a few different kinds of values without knowing what they are ahead of time, Rust asks slightly more of you than many languages do. Dynamic languages will let you pass in anything, of course, as long as the code works when it's run. Java/C# would ask for an interface or a superclass. Duck-typed languages like Go or TypeScript would want some structural type- an object type with a particular set of properties, for instance.

Rust is different. In Rust there are three main approaches for handling this situation, and each has its own advantages and disadvantages.

Reflection in Swift allows us to use the Mirror API to inspect and manipulate arbitrary values at runtime. Even though Swift puts a lot of emphasis on static typing, we can get the flexibility to gain more control over types than you might expect.

In order for one language to cooperate with another usefully via embedded programs in this way, data of some sort needs to be passed between them at runtime, and here there are a few traps with syntax that may catch out unwary shell programmers. We’ll go through a simple example showing the problems, and demonstrate a few potential solutions.