Constants, variables and types

Swift uses let for constants and var for variables. Xcode warns you when a var never changes, so default to let. Swift uses type inference, so let count = 3 is an Int without you saying so.

Swift never converts numbers silently: adding an Int and a Double needs an explicit Double(count). Learn the basic types (Int, Double, Bool, String, Character) and string interpolation, as in "Hello \(name)". let behaves differently for structs and classes.

For a struct, let makes the whole value unchangeable. For a class, it only fixes the reference, so the object itself can still change. That difference is the start of the structs versus classes topic below.