100 exercises to learn Rust

book/src/05_ticket_v2/02_match.md

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+# `match`
+
+You may be wondering—what can you actually **do** with an enum?  
+The most common operation is to **match** on it.
+
+```rust
+enum Status {
+    ToDo,
+    InProgress,
+    Done
+}
+
+impl Status {
+    fn is_done(&self) -> bool {
+        match self {
+            Status::Done => true,
+            // The `|` operator lets you match multiple patterns.
+            // It reads as "either `Status::ToDo` or `Status::InProgress`".
+            Status::InProgress | Status::ToDo => false
+        }
+    }
+}
+```
+
+A `match` statement that lets you compare a Rust value against a series of **patterns**.  
+You can think of it as a type-level `if`. If `status` is an `Done` variant, execute the first block;
+if it's a `InProgress` or `ToDo` variant, execute the second block.
+
+## Exhaustiveness
+
+There's one key detail here: `match` is **exhaustive**. You must handle all enum variants.  
+If you forget to handle a variant, Rust will stop you **at compile-time** with an error.
+
+E.g. if we forget to handle the `ToDo` variant:
+
+```rust
+match self {
+    Status::Done => true,
+    Status::InProgress => false,
+}
+```
+
+the compiler will complain:
+
+```text
+error[E0004]: non-exhaustive patterns: `ToDo` not covered
+ --> src/main.rs:5:9
+  |
+5 |     match status {
+  |     ^^^^^^^^^^^^ pattern `ToDo` not covered
+```
+
+This is a big deal!  
+Codebases evolve over time—you might add a new status down the line, e.g. `Blocked`. The Rust compiler
+will emit an error for every single `match` statement that's missing logic for the new variant.
+That's why Rust developers often sing the praises of "compiler-driven refactoring"—the compiler tells you
+what to do next, you just have to fix what it reports.
+
+## Catch-all
+
+If you don't care about one or more variants, you can use the `_` pattern as a catch-all:
+
+```rust
+match status {
+    Status::Done => true,
+    _ => false
+}
+```
+
+The `_` pattern matches anything that wasn't matched by the previous patterns.
+
+## References
+
+- The exercise for this section is located in `exercises/05_ticket_v2/02_match`