Rust宏教程（翻译）.docVIP

Rust Macros Tutorial 目录 1 Introduction 2 Invocation syntax 3 Transcription syntax 4 Multiplicity 5 Macro argument pattern matching 6 A final note 1. Introduction（介绍） Functions are the primary tool that programmers can use to build abstractions.（函数是程序员用于建立抽象的主要工具。） Sometimes, however, programmers want to abstract over compile-time syntax rather than run-time values.（然而，有时候程序员希望抽象编译期的语法而不是运行期的值。） Macros provide syntactic abstraction.（宏提供语法抽象。） For an example of how this can be useful, consider the following two code fragments, which both pattern-match on their input and both return early in one case, doing nothing otherwise:（用一个例子来解释，宏有多有用，考虑下面两个代码片段，它们都用模式匹配输入然后在唯一的分支中提早返回，不再做别的事情：） match input_1 { special_a(x) = { return x; } _ = {} } // ... match input_2 { special_b(x) = { return x; } _ = {} } This code could become tiresome if repeated many times.（这种代码重复多次是很麻烦的。） However, no function can capture its functionality to make it possible to abstract the repetition away.（然而，无法通过函数来抽象这种重复。） Rusts macro system, however, can eliminate the repetition.（然而，Rust的宏系统可以削除这种重复。） Macros are lightweight custom syntax extensions, themselves defined using the macro_rules! syntax extension.（宏是轻量级的用户算定义语法扩展，使用macro_rules! 语法扩展来定义。） The following early_return macro captures the pattern in the above code:（下面的early_return宏抓住了上面代码的模式：） macro_rules! early_return( ($inp:expr $sp:ident) = ( // invoke it like `(input_5 special_e)` match $inp { $sp(x) = { return x; } _ = {} } ); ) // ... early_return!(input_1 special_a); // ... early_return!(input_2 special_b); Macros are defined in pattern-matching style: in the above example, the text ($inp:expr $sp:ident) that appears on the left-hand side of the = is the macro invocation syntax, a pattern denoting how to write a call to the macro.（宏使用模式匹配定义：上例中，出现在 = 左侧的 ($inp:expr $sp:ident) 是宏调用语法，模式表示怎样调用宏。） The text on the right-hand side of the =, beginning with match $inp, is the macro tr