impl Fields

fn iter(&self) -> Iter<'_, Field>

Get an iterator over the borrowed Field items in this object. This iterator can be used to iterate over a named or unnamed struct or variant's fields uniformly.

fn iter_mut(&mut self) -> IterMut<'_, Field>

Get an iterator over the mutably borrowed Field items in this object. This iterator can be used to iterate over a named or unnamed struct or variant's fields uniformly.

fn len(&self) -> usize

Returns the number of fields.

fn is_empty(&self) -> bool

Returns true if there are zero fields.

fn members(&self) -> Members<'_>

Get an iterator over the fields of a struct or variant as Members. This iterator can be used to iterate over a named or unnamed struct or variant's fields uniformly.

Example

The following is a simplistic Clone derive for structs. (A more complete implementation would additionally want to infer trait bounds on the generic type parameters.)

# use quote::quote;
#
fn derive_clone(input: &syn::ItemStruct) -> proc_macro2::TokenStream {
    let ident = &input.ident;
    let members = input.fields.members();
    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
    quote! {
        impl #impl_generics Clone for #ident #ty_generics #where_clause {
            fn clone(&self) -> Self {
                Self {
                    #(#members: self.#members.clone()),*
                }
            }
        }
    }
}

For structs with named fields, it produces an expression like Self { a: self.a.clone() }. For structs with unnamed fields, Self { 0: self.0.clone() }. And for unit structs, Self {}.