Type safe

 Swift is a type-safe language. This means that the Swift compiler enforces strong typing rules, which helps prevent common programming errors related to data type mismatches.

 In Swift, every variable and constant must have a specific data type, and once that type is set, it cannot be changed. This helps ensure that the data being used in your program is of the correct type, which can help prevent errors and improve program reliability. 

For example, if you try to assign a string value to an integer variable in Swift, the compiler will generate an error, since these data types can't be implicitly converted:

var myNumber: Int = "42" // This will generate a compile-time error

Similarly, if you try to call a method on an object that doesn't exist, the Swift compiler will generate an error at compile-time, rather than waiting for the error to occur at runtime:

let myString = "Hello, world!"
myString.someMethod() // This will generate a compile-time error

By enforcing strong typing rules, Swift helps prevent common programming errors and can make your code more reliable and easier to maintain.