Closures

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Yesterday we covered Error Handling with ?, if you missed it I’d suggest you check it out first.

Error Handling with ?

Imagine you’re writing a web server that processes user requests. Each request needs to be handled based on some condition, like checking if a user is logged in.

Instead of writing a separate function for every possible check, you can use a closure , a small, anonymous function that grabs variables from its surroundings and runs when called.

Closures in Rust are like portable snippets of logic that carry their context with them, making your code more modular and reusable.

In Rust, a closure looks like this: |x| x + 1. It’s a function without a name, defined inline, that takes an argument x and returns x + 1.

But what makes closures special is their ability to “capture” variables from the scope they’re defined in. Let’s see this in action with a real-world-inspired example.

Suppose you’re building a logging system for a Rust application. You want to log messages with a custom prefix, like the name of the module generating the log.