概述

下面几个页面中将介绍重新设计后的 Scala 元编程。它们引入了以下基本设施：

1. inline 是一个新的修饰符，它保证定义在使用时被内联。 内联的主要目的是用来减少函数调用与值访问背后的开销。 展开由 Scala 编译器在 Typer 编译器阶段中执行。与其他一些 ecosystems 中的内联不同， Scala 中的 inline 不仅仅是对编译器的请求，而是一个命令。 这是因为 Scala 中的内联可以驱动其他编译时操作，譬如内联模式匹配（启用类型级编程）、 宏（enabling compile-time, generative, metaprogramming）和运行时代码生成（multi-stage programming）。

2. 宏建立在两个熟悉的基本操作上：引述（quotation）和拼接（splicing）。 引述将程序代码转换为数据，明确来说是这段代码的（树状）表示形式。 表达式用 '{...} 来表示，类型用 '[...] 来表示。拼接使用 ${}' 表示， 它的作用与引述相反：它将程序的表示形式转换为程序代码。结合内联， 这两种抽象允许以编程的方式构造程序代码。

3. Runtime Staging Where macros construct code at compile-time, staging lets programs construct new code at runtime. That way, code generation can depend not only on static data but also on data available at runtime. This splits the evaluation of the program in two or more phases or … stages. Consequently, this method of generative programming is called “Multi-Stage Programming”. Staging is built on the same foundations as macros. It uses quotes and splices, but leaves out inline.

4. Reflection Quotations are a “black-box” representation of code. They can be parameterized and composed using splices, but their structure cannot be analyzed from the outside. TASTy reflection gives a way to analyze code structure by partly revealing the representation type of a piece of code in a standard API. The representation type is a form of typed abstract syntax tree, which gives rise to the TASTy moniker.

5. TASTy Inspection Typed abstract syntax trees are serialized in a custom compressed binary format stored in .tasty files. TASTy inspection allows to load these files and analyze their content’s tree structure.

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