rust-macro

Development

宏与过程元编程专家。处理 macro_rules!, derive, proc-macro, 泛型宏、编译时计算等问题。触发词：macro, derive, proc-macro, macro_rules, 宏, 过程宏, 编译时计算

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宏与过程元编程

核心问题

如何减少重复代码？什么时候用宏，什么时候用泛型？

宏是编译时代码生成，泛型是运行时多态。

宏 vs 泛型

维度	宏	泛型
灵活性	代码转换	类型抽象
编译开销	增量编译友好	单态化开销
错误信息	可能难懂	清晰
调试	调试宏展开代码	直接调试
使用场景	减少样板	通用算法

declarative macros (macro_rules!)

基本结构

macro_rules! my_vec {
    () => {
        Vec::new()
    };
    ($($elem:expr),*) => {
        vec![$($elem),*]
    };
    ($elem:expr; $n:expr) => {
        vec![$elem; $n]
    };
}

重复模式

标记	含义
`$()`	匹配零个或多个
`$($x),*`	以逗号分隔
`$($x),+`	至少一个
`$x:ty`	类型匹配
`$x:expr`	表达式匹配
`$x:pat`	模式匹配

派生宏 (derive macro)

实现简单 derive

use proc_macro::TokenStream;
#[proc_macro_derive(MyDerive)]
pub fn my_derive(input: TokenStream) -> TokenStream {
    let input = syn::parse_macro_input!(input as syn::DeriveInput);
    let name = &input.ident;
    
    let expanded = quote::quote! {
        impl MyDerive for #name {
            fn my_method(&self) -> String {
                format!("Hello from {}", stringify!(#name))
            }
        }
    };
    
    expanded.into()
}

使用

#[derive(MyDerive)]
struct MyStruct {
    field: i32,
}

函数式过程宏

#[proc_macro]
pub fn my_func_macro(input: TokenStream) -> TokenStream {
    // 转换输入
    let tokens = input.into_iter().collect::<Vec<_>>();
    // 生成代码
    quote::quote! { /* ... */ }.into()
}

调试宏

# 查看宏展开结果
cargo expand
cargo expand --test test_name

最佳实践

做法	原因
先用泛型	泛型更安全、更易调试
宏保持简单	复杂宏难维护
文档化宏	用户需要理解展开行为
测试展开结果	确保正确性
用 cargo expand 调试	可视化宏展开

常用 crate

crate	用途
`syn`	解析 Rust 代码
`quote`	生成 Rust 代码
`proc-macro2`	Token 处理
`derive-more`	常用 derive 宏