ios - Swift 中无法解释的关键字 : left, 无，对，类型。他们在做什么？

Question

我一直在阅读 Apple 的 Swift 编程语言书籍(针对 Swift 2.0 更新的版本)，我发现了一些非常奇怪的东西。在 Language Reference > Lexical Stricture > Keywords and Punctuation(link here - 但你需要向下滚动一点)有一个语言列表关键字。其中一些在任何地方都没有解释。

Keywords reserved in particular contexts: associativity, convenience, dynamic, didSet, final, get, infix, inout, lazy, left, mutating, none, nonmutating, optional, override, postfix, precedence, prefix, Protocol, required, right, set, Type, unowned, weak, and willSet. Outside the context in which they appear in the grammar, they can be used as identifiers.

您知道它们的作用/含义或在哪里可以找到适用信息吗？

Answer 1

left、right 和none 用于指定自定义运算符的结合性:

The associativity of an operator specifies how a sequence of operators with the same precedence level are grouped together in the absence of grouping parentheses. You specify the associativity of an operator by writing the context-sensitive keyword associativity followed by the associativity, which is one of the context-sensitive keywords left, right, or none.

https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/associativity

Type 与元类型一起使用:

A metatype type refers to the type of any type, including class types, structure types, enumeration types, and protocol types.

The metatype of a class, structure, or enumeration type is the name of that type followed by .Type.

https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/metatype-type