Enum syn::Fields

pub enum Fields {
    Named(FieldsNamed),
    Unnamed(FieldsUnnamed),
    Unit,
}

Data stored within an enum variant or struct.

Syntax tree enum

This type is a syntax tree enum.

Variants

Named(FieldsNamed)

Named fields of a struct or struct variant such as Point { x: f64, y: f64 }.

Unnamed(FieldsUnnamed)

Unnamed fields of a tuple struct or tuple variant such as Some(T).

Unit

Unit struct or unit variant such as None.

Implementations

impl Fields

pub 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.

pub 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.

pub fn len(&self) -> usize

Returns the number of fields.

pub fn is_empty(&self) -> bool

Returns true if there are zero fields.

pub 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.)

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 {}.

Trait Implementations

impl Clone for Fields

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl From<FieldsNamed> for Fields

fn from(e: FieldsNamed) -> Fields

Converts to this type from the input type.

impl From<FieldsUnnamed> for Fields

fn from(e: FieldsUnnamed) -> Fields

Converts to this type from the input type.

impl<'a> IntoIterator for &'a Fields

type Item = &'a Field

The type of the elements being iterated over.

type IntoIter = Iter<'a, Field>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<'a> IntoIterator for &'a mut Fields

type Item = &'a mut Field

The type of the elements being iterated over.

type IntoIter = IterMut<'a, Field>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl IntoIterator for Fields

type Item = Field

The type of the elements being iterated over.

type IntoIter = IntoIter<Field>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl ToTokens for Fields

fn to_tokens(&self, tokens: &mut TokenStream)

Write self to the given TokenStream.

fn to_token_stream(&self) -> TokenStream

Convert self directly into a TokenStream object.

fn into_token_stream(self) -> TokenStream

where Self: Sized,

Convert self directly into a TokenStream object.