Hello again!
I started playing with proc_macro and I'm trying to a macro that maps fields of struct A into struct B. If there are optional fields in struct A, it checks that are not None. If are not not are mapped into struct B otherwise an error is returned. I think I'm mostly there but I'm encountering the error in the title
mismatched types expected HasIterator, found ThereIsNoIteratorInRepetition`` and I don't know how to solve it. the error is at let gen = quote! {
use proc_macro::TokenStream;
use quote::quote;
use syn::{self, Data, DeriveInput, Fields, Ident};
#[proc_macro_derive(WopStructs)]
pub fn wop_structs(input: TokenStream) -> TokenStream {
let ast = syn::parse(input).unwrap();
impl_wop_structs(&ast)
}
fn impl_wop_structs(ast: &syn::DeriveInput) -> TokenStream {
let struct_name = &ast.ident;
let fields = match &ast.data {
Data::Struct(data) => match &data.fields {
Fields::Named(fields) => &fields.named,
_ => {
return quote! {
compile_error!("WopStructs only supports structs with named fields.");
}
.into();
}
},
_ => {
return quote! {
compile_error!("WopStructs only supports named fields in structs.");
}
.into();
}
};
let gen = quote! {
impl #struct_name {
fn wop(&mut self, other: Self) -> Result<(), &'static str> {
let other = other;
#(if let Some(val) = other.#fields {
if let Some(ref mut field) = self.#fields {
*field = val;
} else {
return Err("Required field is None");
}
})*
Ok(())
}
}
};
gen.into()
}