2022-11-14：rust 语言，请使用过程宏给结构体 AAA 生成结构体 AAABuilder 和创建 AAABuilder 实例的方法。宏使用如下： #[derive(Builder)] pub stru

2022-11-14
北京
本文字数：2013 字
阅读完需：约 7 分钟

2022-11-14：rust 语言，请使用过程宏给结构体 AAA 生成结构体 AAABuilder 和创建 AAABuilder 实例的方法。宏使用如下：

#[derive(Builder)]pub struct AAA {    a: String,    b: i32,       c: f64,    d: Vec<bool>,}

复制代码

宏展开后变成如下代码：

pub struct AAA {    a: String,    b: i32,       c: f64,    d: Vec<bool>,}pub struct AAABuilder {    a: std::option::Option<String>,    b: std::option::Option<i32>,    c: std::option::Option<f64>,    d: std::option::Option<Vec<bool>>,}impl AAA {    pub fn builder() -> AAABuilder {        AAABuilder {            a: std::option::Option::None,            b: std::option::Option::None,            c: std::option::Option::None,            d: std::option::Option::None,        }    }}

复制代码

答案 2022-11-14：

这题没啥技巧，自然智慧即可。

代码用 rust 编写。代码如下：

// builder/src/lib.rsuse proc_macro::TokenStream;use quote;use syn::spanned::Spanned;#[proc_macro_derive(Builder)]pub fn derive(input: TokenStream) -> TokenStream {    let st = syn::parse_macro_input!(input as syn::DeriveInput);    match expand_code(&st) {        Ok(token_stream) => token_stream.into(),        Err(e) => e.to_compile_error().into(),    }}
fn get_fields(    st: &syn::DeriveInput,) -> syn::Result<&syn::punctuated::Punctuated<syn::Field, syn::Token![,]>> {    if let syn::Data::Struct(syn::DataStruct {        fields: syn::Fields::Named(syn::FieldsNamed { ref named, .. }),        ..    }) = st.data    {        return Ok(named);    };    Err(syn::Error::new_spanned(st, "必须定义在结构体上"))}
fn gen_fields(st: &syn::DeriveInput) -> syn::Result<proc_macro2::TokenStream> {    let fields = get_fields(st)?;    let idents: Vec<_> = fields.iter().map(|f| &f.ident).collect();    let types: Vec<_> = fields.iter().map(|f| &f.ty).collect();    let ret = quote::quote!(        #( #idents: std::option::Option<#types>),*    );    return Ok(ret);}
fn gen_init_clauses(st: &syn::DeriveInput) -> syn::Result<Vec<proc_macro2::TokenStream>> {    let fields = get_fields(st)?;    let init_cluase: Vec<_> = fields        .iter()        .map(|f| {            let ident = &f.ident;            quote::quote!(                #ident: std::option::Option::None            )        })        .collect();    Ok(init_cluase)}
fn expand_code(st: &syn::DeriveInput) -> syn::Result<proc_macro2::TokenStream> {    let struct_name_literal = st.ident.to_string();    let builder_name_literal = format!("{}Builder", struct_name_literal);    let builder_name_ident = syn::Ident::new(&builder_name_literal, st.span());    let struct_ident = &st.ident;    let builder_struct_field_def = gen_fields(st)?;    let builder_struct_factory_init_clauses = gen_init_clauses(st)?;    let ret = quote::quote!(        pub struct #builder_name_ident{            #builder_struct_field_def        }
        impl #struct_ident {            pub fn builder() -> #builder_name_ident {                #builder_name_ident {                    #(#builder_struct_factory_init_clauses),*                }            }        }    );    Ok(ret)}

复制代码

# builder.Cargo.toml[package]name = "derive_builder"version = "0.0.0"autotests = falseedition = "2021"publish = false
[lib]proc-macro = true
[[test]]name = "tests"path = "tests/progress.rs"
[dev-dependencies]trybuild = { version = "1.0.49", features = ["diff"] }
[dependencies]syn = {version="1.0",features=["extra-traits"]}proc-macro2 = {version="1.0"}quote = {version="1.0"}

复制代码

use derive_builder::Builder;
#[derive(Builder)]pub struct AAA {    a: String,    b: i32,    c: f64,    d: Vec<bool>,}
fn main() {    let builder = AAA::builder();
    let _ = builder;}

复制代码

# Cargo.toml[package]name = "proc-macro-workshop"version = "0.0.0"edition = "2021"publish = false
[workspace]
[[bin]]name = "workshop"path = "main.rs"
[dependencies]bitfield = { path = "bitfield" }derive_builder = { path = "builder" }derive_debug = { path = "debug" }seq = { path = "seq" }sorted = { path = "sorted" }