100 exercises to learn Rust

book/src/06_ticket_management/03_resizing.md

@@ -0,0 +1,25 @@
+# Resizing
+
+We said that `Vec` is a "growable" vector type, but what does that mean?
+What happens if you try to insert an element into a `Vec` that's already at maximum capacity?
+
+```rust
+let mut numbers = Vec::with_capacity(3);
+numbers.push(1);
+numbers.push(2);
+numbers.push(3); // Max capacity reached
+numbers.push(4); // What happens here?
+```
+
+The `Vec` will **resize** itself.  
+It will ask the allocator for a new (larger) chunk of heap memory, copy the elements over, and deallocate the old memory.
+
+This operation can be expensive, as it involves a new memory allocation and copying all existing elements.  
+
+## `Vec::with_capacity`
+
+If you have a rough idea of how many elements you'll store in a `Vec`, you can use the `Vec::with_capacity` 
+method to pre-allocate enough memory upfront.  
+This can avoid a new allocation when the `Vec` grows, but it may waste memory if you overestimate actual usage.
+
+Evaluate on a case-by-case basis.