Add example of using Fields::members iterator

src/data.rs

@@ -108,6 +108,35 @@ impl Fields {
     /// Get an iterator over the fields of a struct or variant as [`Member`]s.
     /// 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 {}`.
     pub fn members(&self) -> impl Iterator<Item = Member> + Clone + '_ {
         struct Members<'a> {
             fields: punctuated::Iter<'a, Field>,