postgres_derives/
lib.rs

1use proc_macro::{self, TokenStream};
2use quote::quote;
3use syn::{parse_macro_input, DeriveInput, Data, DataStruct, Fields};
4
5#[proc_macro_derive(FromRow)]
6pub fn from_row(input: TokenStream) -> TokenStream {
7    let input = parse_macro_input!(input as DeriveInput);
8
9    // get the name of the type we want to implement the trait for
10    let name = &input.ident;
11
12    let fields = match &input.data {
13        Data::Struct(DataStruct { fields: Fields::Named(fields), .. }) => &fields.named,
14        _ => panic!("expected a struct with named fields"),
15    };
16    let field_name = fields.iter().map(|field| &field.ident);
17    let field_type = fields.iter().enumerate().map(|(i, _)| i);
18  
19    // println!("{:?}", input.);
20
21    let expanded = quote! {
22        impl #name {
23            pub fn from_row(row: Row) -> #name {
24                #name {
25                    #(
26                        #field_name: row.get(#field_type),
27                    )*
28                }
29            }
30        }
31    };
32  
33    TokenStream::from(expanded)
34}