Add old edits on draft from August 4

content/posts/handling-multiple-possible-errors-in-rust.md

@@ -0,0 +1,81 @@
+---
+title: "Handling Multiple Possible Errors in Rust"
+date: 2022-08-04
+tags:
+  - programming
+draft: true
+---
+
+## Background
+
+Rust handles errors better than any other language I’ve ever used. All possible errors are known at build time, and by design Rust forces you to at a bare minimum *acknowledge* that these errors are possible with `.unwrap()`, otherwise writing specific error handling logic.
+
+### The `Result` enum
+
+All of this is thanks to the `Result` enum, which is defined as follows:
+
+```RS
+enum Result<T, E> {
+   Ok(T),
+   Err(E),
+}
+```
+
+`Result` is a generic type that requires two type parameters, `T`, the actual value the result is wrapping, and `E`, the error type in case something goes wrong. In the success case, the `Ok(T)` variant will be used, and in an error case, `Err(E)` will be used.
+
+What makes this powerful is the fact that since `Result` wraps the actual result value, access to that value is prevented unless the possibility of an error is acknowledged.
+
+### Handling `Result`
+
+For the sake of example, say we’re writing a theoretical function, `acquire_banana`, that drives to the store, purchases a banana, and returns the banana.
+
+We have a function called `drive_to_store`. It returns a `Result` that can either be nothing `()`, or a `NavigationError`.
+
+```RS
+fn drive_to_store() -> Result<(), NavigationError> { ... }
+```
+
+We then have the following function, `acquire_banana`. It also returns a `Result`, but this time it can either be a `Banana` or a `PurchaseError`.
+
+```RS
+fn purchase_banana() -> Result<Banana, PurchaseError> { ... }
+```
+
+In other languages, we might write the function something like this:
+
+```RS
+fn acquire_banana() -> Banana {
+    drive_to_store();
+    purchase_banana()
+}
+```
+
+However, this doesn’t work in Rust. There are two issues here. First, while `drive_to_store();` is in theory valid code (it returns an enum that we ignore), `Result`s **must** be handled. Otherwise, you will get compile warnings. Second, we cannot return `purchase_banana` from the function, because its return type is `Result<Banana, PurchaseError>`, not `Banana`.
+
+The naïve solution to this would be using the `unwrap` method on the `Result`s, like this:
+
+```RS
+fn acquire_banana() -> Banana {
+    drive_to_store().unwrap();
+    purchase_banana().unwrap()
+}
+```
+
+The `.unwrap()` method does exactly what it sounds like. If a `Result` is the `Ok(T)` variant, it returns `T`. However, the naïvety here lies in what happens on the `Err(E)` variant. In that case, it *panics*, printing the error and kills the thread/program. A well-designed program should take errors into account, so this solution is unacceptable.
+
+The best solution is in this case is **error propagation** using the question mark `?` operator. It works similarly to `.unwrap()`, but instead of panicking on the `Err(E)` case, it returns `Err(E)` from the function. This lets you quickly unwrap results without convoluted `match` statements.
+
+This lets you convert this:
+
+```RS
+let x = match get_result() {
+    Ok(value) => value,
+    Err(error) => return Err(error),
+};
+```
+
+Into this:
+
+```RS
+let x = get_result()?;
+```