系統關鍵字

Swift 系統內建的關鍵字有以下幾種類型：

Declarations

associatedtype, class, deinit, enum, extension, func, import, init, inout, internal, let, operator, private, protocol, public, static, struct, subscript, typealias, var.

Statements

break, case, continue, default, defer, do, else, fallthrough, for, guard, if, in, repeat, return, switch, where, while.

Expressions and types

as, catch, dynamicType, false, is, nil, rethrows, super, self, Self, throw, throws, true, try, #column, #file, #function, #line.

Particular contexts

associativity, convenience, dynamic, didSet, final, get, infix, indirect, lazy, left, mutating, none, nonmutating, optional, override, postfix, precedence, prefix, Protocol, required, right, set, Type, unowned, weak, willSet.

命名

不建議使用系統內建的關鍵字來命名變數、常數、函式、類別及其他自定義的型別，如果真的一定要使用的話，必須以一對反引號` 把名稱包起來，如下：

// 無法這樣命名 這行會報錯誤
let class = 20

// 必須以一對反引號 ` 包起名稱
var `class` = 12

// 使用也必須加上反引號
print("It is \(`class`)")