how to synthesize vars

To synthesize variables in Swift, you can use the var keyword to declare mutable variables. Here are some key points from the WWDC sessions that might help:

Declaring Variables:
- Use var to declare a mutable variable.
- Use let to declare an immutable variable.
- Example:
```
var x = 10
let y = 20
```
Handling Mutability:
- If you want to ensure a variable does not change, use let instead of var. This guarantees immutability.
- Example from A Swift Tour: Explore Swift’s features and design:
```
let username = "Alice"
```
Memory Management:
- When a var is captured by an escaping closure, its lifetime is extended, and it may need to be heap allocated.
- Example from Explore Swift performance:
```
var capturedVar = 10
let closure = { [capturedVar] in
    print(capturedVar)
}
```
Concurrency and Data Races:
- Switching a var to a let can help avoid data races in concurrent code.
- Example from Migrate your app to Swift 6:
```
let safeVar = 10
```
Optimizing Performance:
- Swift can optimize variable usage to avoid unnecessary copies, especially with value types like arrays.
- Example from Explore Swift performance:
```
var array = [1, 2, 3]
var anotherArray = array
```

For more detailed information, you can refer to the sessions mentioned above.