100 exercises to learn Rust

book/src/05_ticket_v2/03_variants_with_data.md

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+# Variants can hold data 
+
+```rust
+enum Status {
+    ToDo,
+    InProgress,
+    Done,
+}
+```
+
+Our `Status` enum is what's usually called a **C-style enum**.  
+Each variant is a simple label, a bit like a named constant. You can find this kind of enum in many programming 
+languages, like C, C++, Java, C#, Python, etc.
+
+Rust enums can go further though. We can **attach data to each variant**.
+
+## Variants
+
+Let's say that we want to store the name of the person who's currently working on a ticket.  
+We would only have this information if the ticket is in progress. It wouldn't be there for a to-do ticket or 
+a done ticket. 
+We can model this by attaching a `String` field to the `InProgress` variant:
+
+```rust
+enum Status {
+    ToDo,
+    InProgress {
+        assigned_to: String,
+    },
+    Done,
+}
+```
+
+`InProgress` is now a **struct-like variant**.  
+The syntax mirrors, in fact, the one we used to define a struct—it's just "inlined" inside the enum, as a variant.
+
+## Accessing variant data
+
+If we try to access `assigned_to` on a `Status` instance,
+
+```rust
+let status: Status = /* */;
+
+// This won't compile
+println!("Assigned to: {}", status.assigned_to);
+```
+
+the compiler will stop us:
+
+```text
+error[E0609]: no field `assigned_to` on type `Status`
+ --> src/main.rs:5:40
+  |
+5 |     println!("Assigned to: {}", status.assigned_to);
+  |                                        ^^^^^^^^^^^ unknown field
+```
+
+`assigned_to` is **variant-specific**, it's not available on all `Status` instances.  
+To access `assigned_to`, we need to use **pattern matching**:
+
+```rust
+match status {
+    Status::InProgress { assigned_to } => {
+        println!("Assigned to: {}", assigned_to);
+    },
+    Status::ToDo | Status::Done => {
+        println!("Done");
+    }
+}
+```
+
+## Bindings
+
+In the match pattern `Status::InProgress { assigned_to }`, `assigned_to` is a **binding**.  
+We're **destructuring** the `Status::InProgress` variant and binding the `assigned_to` field to 
+a new variable, also named `assigned_to`.  
+If we wanted, we could bind the field to a different variable name:
+
+```rust
+match status {
+    Status::InProgress { assigned_to: person } => {
+        println!("Assigned to: {}", person);
+    },
+    Status::ToDo | Status::Done => {
+        println!("Done");
+    }
+}
+```
+
+## References
+
+- The exercise for this section is located in `exercises/05_ticket_v2/03_variants_with_data`