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

Posted 2022-12-08 福大大架构师每日一题

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>,

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,
        
    

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.rs
use 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)

# builder.Cargo.toml
[package]
name = "derive_builder"
version = "0.0.0"
autotests = false
edition = "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"

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;

# 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" 

敲cargo expand命令后，打印如下：