Rust特性总结——#[]

# Rust的#[]特性 ## 条件编译——#[cfg()] #[cfg()]是Rust的条件编译机制，允许根据不同条件选择性编译代码。 ### 基本语法 ```rust #[cfg(condition)] fn some_funtion(){ //只有条件满足才编译这个函数 } ``` ### 常用条件类型 #### 1. 目标操作系统(target_os) ```rust #[cfg(target_os = "windows")] fn windows_specific_function(){ //只有在windows系统上才编译 println!("这个函数只在windows系统编译"); } #[cfg(target_os = "linux")] fn linux_specific_function(){ // 只有在linux系统上才编译 println!("这个函数只在linux系统上编译"); } #[cfg(target_os = "macos")] fn macos_specific_function(){ println!("这个函数只在macOS上编译"); } // 使用示例 fn main(){ #[cfg(target_os = "windows")] { println!("运行在WIndows系统上"); windows_specification_function(); } #[cfg(target_os = "linux")] { println!("运行在Linux系统上"); linux_specification_function(); } } ``` #### 2. 目标架构(target_arch) ```rust #[cfg(target_arch = "x86_x64")] fn x64_optimized_function(){ println!("针对x86_x64架构优化的函数"); } #[cfg(target_arch = "aarch64")] fn arm64_optimized_function(){ println!("针对ARM64架构优化的函数"); } #[cfg(target_arch = "wasm32")] fn wasm_function(){ println!("WebAssembly专用函数"); } ``` #### 3. 编译模式(debug_assertions) ```rust #[cfg(debug_assertions)] fn debug_only_function(){ println!("这个函数只在debug模式下编译"); } #[cfg(not(debug_assertions))] fn release_only_function(){ println!("这个函数只在release模式下编译"); } fn main() { #[cfg(debug_assertions)] println!("当前是debug模式"); #[cfg(not(debug_assertions))] println!("当前是release模式"); } ``` #### 4. 功能特性(feature) ```rust // 在Cargo.toml中定义[feature],格式如下： // [feature] // networking = [] // database = [] // default = ["networking"] #[cfg(feature = "networking")] mod networking() { pub fn send_request(){ println!("发送网络请求"); } } #[cfg(feature = "database")] mod database{ pub fn database() { println!("连接数据库"); } } #[cfg(all(feature = "networking", feature = "database"))] fn full_stack_function(){ println!("需要网络和数据库功能"); } ``` # 逻辑组合 ## 1. `all()` - 所有条件都必须满足 ```rust #[cfg(all(target_os = "linux", target_arch = "x86_64"))] fn linux_x64_function() { println!("只在 Linux x86_64 上编译"); } #[cfg(all(feature = "ssl", not(debug_assertions)))] fn secure_release_function() { println!("需要 SSL 功能且在 release 模式"); } ``` ## 2. `any()` - 任一条件满足即可 ```rust #[cfg(any(target_os = "linux", target_os = "macos"))] fn unix_like_function() { println!("在类 Unix 系统上编译"); } #[cfg(any(feature = "mysql", feature = "postgresql"))] fn database_function() { println!("支持任一数据库"); } ``` ## 3. `not()` - 条件不满足时 ```rust #[cfg(not(target_os = “windows”))] fn non_windows_function(){ println!("非windows系统"); } #[cfg(not(featrue = "std")] fn no_std_funtion(){ println!("无标准库环境"); } ``` # 实际应用示例 ## 1. 平台特定的文件操作 ```rust use std::path::Path; #[cfg(target_os = "windows")] fn get_config_dir() -> &'static str { "C:\\ProgramData\\MyApp" } #[cfg(target_os = "linux")] fn get_config_dir() -> &'static str { "/etc/myapp" } #[cfg(target_os = "macos")] fn get_config_dir() -> &'static str { "/Library/Application Support/MyApp" } // 使用配置目录 fn load_config() { let config_path = get_config_dir(); println!("配置文件路径: {}", config_path); } ``` ## 2. 调试和发布版本的不同行为 ```rust struct Logger; impl Logger { #[cfg(debug_assertions)] fn log(&self, message: &str) { println!("[DEBUG] {}: {}", chrono::Utc::now(), message); } #[cfg(not(debug_assertions))] fn log(&self, message: &str) { // 在 release 版本中可能写入文件或发送到日志服务 eprintln!("[INFO] {}", message); } } // 条件编译的宏 macro_rules! debug_println { ($($arg:tt)*) => { #[cfg(debug_assertions)] println!($($arg)*); }; } fn main() { let logger = Logger; logger.log("应用程序启动"); debug_println!("这条消息只在 debug 模式显示"); } ``` ## 3. 功能特性的条件编译 ```rust // Cargo.toml // [features] // json_support = ["serde_json"] // xml_support = ["quick-xml"] // default = ["json_support"] pub enum DataFormat { #[cfg(feature = "json_support")] Json, #[cfg(feature = "xml_support")] Xml, Plain, } pub struct DataProcessor; impl DataProcessor { #[cfg(feature = "json_support")] pub fn process_json(&self, data: &str) -> Result<String, Box<dyn std::error::Error>> { // 使用 serde_json 处理 Ok(format!("JSON 处理结果: {}", data)) } #[cfg(feature = "xml_support")] pub fn process_xml(&self, data: &str) -> Result<String, Box<dyn std::error::Error>> { // 使用 quick-xml 处理 Ok(format!("XML 处理结果: {}", data)) } pub fn process(&self, data: &str, format: DataFormat) -> Result<String, Box<dyn std::error::Error>> { match format { #[cfg(feature = "json_support")] DataFormat::Json => self.process_json(data), #[cfg(feature = "xml_support")] DataFormat::Xml => self.process_xml(data), DataFormat::Plain => Ok(data.to_string()), } } } ``` ## 4. 测试代码的条件编译 ```rust pub fn add(a: i32, b: i32) -> i32 { a + b } #[cfg(test)] mod tests { use super::*; #[test] fn test_add() { assert_eq!(add(2, 3), 5); } #[cfg(feature = "extended_tests")] #[test] fn test_add_extended() { assert_eq!(add(-1, 1), 0); assert_eq!(add(0, 0), 0); } } // 基准测试（需要 nightly 版本） #[cfg(all(test, feature = "bench"))] mod benches { use super::*; use test::Bencher; #[bench] fn bench_add(b: &mut Bencher) { b.iter(|| add(1, 2)); } } ``` # 自定义配置 ## 1. 环境变量条件 ```rust // 通过环境变量控制编译 #[cfg(env = "CUSTOM_BUILD")] fn custom_build_function() { println!("自定义构建版本"); } // 在构建时设置: CUSTOM_BUILD=1 cargo build ``` ## 2. 自定义 cfg 标志 ```rust // 在 build.rs 中设置自定义标志 // println!("cargo:rustc-cfg=custom_feature"); #[cfg(custom_feature)] fn custom_feature_function() { println!("自定义功能已启用"); } ``` # 最佳实践 ## 1. 避免代码重复 ```rust // 不好的做法 #[cfg(target_os = "windows")] fn get_separator() -> char { '\\' } #[cfg(not(target_os = "windows"))] fn get_separator() -> char { '/' } // 更好的做法 fn get_separator() -> char { #[cfg(target_os = "windows")] return '\\'; #[cfg(not(target_os = "windows"))] return '/'; } ``` ## 2. 使用 cfg\_if 宏简化复杂条件 ```rust use cfg_if::cfg_if; cfg_if! { if #[cfg(target_os = "windows")] { fn platform_specific_code() { println!("Windows 特定代码"); } } else if #[cfg(target_os = "linux")] { fn platform_specific_code() { println!("Linux 特定代码"); } } else { fn platform_specific_code() { println!("其他平台代码"); } } } ``` ## 3. 文档中标注条件 ```rust /// 这个函数只在启用网络功能时可用 /// /// # Examples /// /// ```rust /// # #[cfg(feature = "networking")] /// use myapp::send_data; /// /// # #[cfg(feature = "networking")] /// send_data("Hello, world!"); /// ``` #[cfg(feature = "networking")] pub fn send_data(data: &str) { println!("发送数据: {}", data); } ```