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//! Multiplicity of fields (Items and Arguments)
//!
//! This module supports type-based handling of multiplicity,
//! of Items (within Documents) and Arguments (in Item keyword lines).
//! It is **for use by macros**, rather than directly.
//! See also `encode::multiplicity` which is the corresponding module for encoding.
//! # Explanation
//! We use autoref specialisation to allow macros to dispatch to
//! trait impls for `Vec<T: ItemValueParseable>`, `Option<T>` etc.
//! as well as simply unadorned `T`.
//! We implement traits on a helper type `struct `[`MultiplicitySelector<Field>`].
//! For Items we have `trait `[`ItemSetMethods`].
//! `ItemSetMethods` is implemented for `MultiplicitySelector<Field>`
//! for each supported `Field`.
//! So, for `MultiplicitySelector<T>`, `MultiplicitySelector<Option<T>>`, and `MultiplicitySelector<Vec<T>>`.
//! *But*, for just `T`, the impl is on `&MultiplicitySelector<T>`.
//! When methods on `MultiplicitySelector` are called, the compiler finds
//! the specific implementation for `MultiplicitySelector<Option<_>>` or `..Vec<_>`,
//! or, failing that, derefs and finds the blanket impl on `&MultiplicitySelector<T>`.
//! For Arguments we have [`ArgumentSetMethods`],
//! and for Objects, [`ObjectSetMethods`],
//! which work similarly.
//! (We need separate traits for each of the kinds of netdoc element,
//! for good support of inference in the derive macro.
//! Type inference is particularly difficult during parsing, since we need the type
//! information to flow from the field type, which is the *destination*
//! to which a value is going to be stored.)
use super::*;
/// Helper type that allows us to select an impl of `ItemSetMethods` etc.
///
/// **For use by macros**.
/// See the [module-level docs](multiplicity).
/// This is distinct from `encode::MultiplicitySelector`,
/// principally because it has the opposite variance.
#[derive(Educe)]
#[educe(Clone, Copy, Default)]
pub struct MultiplicitySelector<Field>(PhantomData<fn() -> Field>);
/// Methods for handling some multiplicity of Items, during parsing
/// During parsing, we accumulate into a value of type `Option<Self::Field>`.
/// The semantics of this are item-set-implementation-dependent;
/// using a type which is generic over the field type in a simple way
/// allows the partially-parsed accumulation state for a whole netdoc to have a concrete type.
/// See the [module-level docs](multiplicity), and
/// [Field type in `NetdocParseable`](derive_deftly_template_NetdocParseable#field-type).
/// # Example
/// The code in the (derive) macro output is roughly like this:
/// ```
/// use tor_netdoc::parse2::multiplicity::{MultiplicitySelector, ItemSetMethods as _};
/// let selector = MultiplicitySelector::<Vec<i32>>::default();
/// let mut accum = None;
/// selector.accumulate(&mut accum, 12).unwrap();
/// let out = selector.finish(accum, "item-set").unwrap();
/// assert_eq!(out, [12]);
//
// When implementing this, update the documentation in the `NetdocParseable` derive.
pub trait ItemSetMethods: Copy + Sized {
/// The value for each Item.
type Each: Sized;
/// The output type: the type of the field in the netdoc struct.
type Field: Sized;
/// Can we accumulate another item ?
/// Can be used to help predict whether `accumulate` will throw.
fn can_accumulate(self, acc: &Option<Self::Field>) -> Result<(), EP>;
/// Accumulate one value into the accumulator.
fn accumulate(self, acc: &mut Option<Self::Field>, one: Self::Each) -> Result<(), EP>;
/// Resolve the accumulator into the output.
fn finish(
self,
acc: Option<Self::Field>,
item_keyword: &'static str,
) -> Result<Self::Field, EP>;
/// If the contained type is a sub-document, call its `is_intro_item_keyword`.
fn is_intro_item_keyword(self, kw: KeywordRef<'_>) -> bool
where
Self::Each: NetdocParseable,
{
Self::Each::is_intro_item_keyword(kw)
}
/// If the contained type is a sub-document, call its `is_structural_keyword`.
fn is_structural_keyword(self, kw: KeywordRef<'_>) -> Option<IsStructural>
Self::Each::is_structural_keyword(kw)
/// `finish` for if the contained type is a wsub-document
/// Obtain the sub-document's intro keyword from its `doctype_for_error`.
fn finish_subdoc(self, acc: Option<Self::Field>) -> Result<Self::Field, EP>
self.finish(acc, Self::Each::doctype_for_error())
/// Check that the element type is an Item
/// For providing better error messages when struct fields don't implement the right trait.
/// See `derive.rs`, and search for this method name.
fn check_item_value_parseable(self)
Self::Each: ItemValueParseable,
/// Check that the element type is a Signature
fn check_signature_item_parseable<H>(self, _: &mut H)
Self::Each: SignatureItemParseable,
H: AsMut<<Self::Each as SignatureItemParseable>::HashAccu>,
/// Check that the element type is a sub-document
fn check_subdoc_parseable(self)
/// Check that the element type is an argument
fn check_item_argument_parseable(self)
Self::Each: ItemArgumentParseable,
impl<T> ItemSetMethods for MultiplicitySelector<Vec<T>> {
type Each = T;
type Field = Vec<T>;
// We always have None, or Some(nonempty)
fn can_accumulate(self, _acc: &Option<Vec<T>>) -> Result<(), EP> {
Ok(())
fn accumulate(self, acc: &mut Option<Vec<T>>, item: T) -> Result<(), EP> {
acc.get_or_insert_default().push(item);
fn finish(self, acc: Option<Vec<T>>, _keyword: &'static str) -> Result<Vec<T>, EP> {
Ok(acc.unwrap_or_default())
impl<T: Ord> ItemSetMethods for MultiplicitySelector<BTreeSet<T>> {
type Field = BTreeSet<T>;
fn can_accumulate(self, _acc: &Option<BTreeSet<T>>) -> Result<(), EP> {
fn accumulate(self, acc: &mut Option<BTreeSet<T>>, item: T) -> Result<(), EP> {
if !acc.get_or_insert_default().insert(item) {
return Err(EP::ItemRepeated);
fn finish(self, acc: Option<BTreeSet<T>>, _keyword: &'static str) -> Result<BTreeSet<T>, EP> {
impl<T> ItemSetMethods for MultiplicitySelector<Option<T>> {
type Field = Option<T>;
// We always have None, or Some(Some(_))
fn can_accumulate(self, acc: &Option<Option<T>>) -> Result<(), EP> {
if acc.is_some() {
Err(EP::ItemRepeated)?;
fn accumulate(self, acc: &mut Option<Option<T>>, item: T) -> Result<(), EP> {
self.can_accumulate(acc)?;
*acc = Some(Some(item));
fn finish(self, acc: Option<Option<T>>, _keyword: &'static str) -> Result<Option<T>, EP> {
Ok(acc.flatten())
impl<T> ItemSetMethods for &'_ MultiplicitySelector<T> {
type Field = T;
fn can_accumulate(self, acc: &Option<T>) -> Result<(), EP> {
fn accumulate(self, acc: &mut Option<T>, item: T) -> Result<(), EP> {
*acc = Some(item);
fn finish(self, acc: Option<T>, keyword: &'static str) -> Result<T, EP> {
acc.ok_or(EP::MissingItem { keyword })
/// Method for handling some multiplicity of Arguments
/// [Field type in `ItemValueParseable`](derive_deftly_template_ItemValueParseable#field-type).
/// use tor_netdoc::parse2::multiplicity::{MultiplicitySelector, ArgumentSetMethods as _};
/// use tor_netdoc::parse2::{ItemArgumentParseable, ItemStream, ParseInput};
/// let doc = "intro-item 12 66\n";
/// let input = ParseInput::new(doc, "<literal>");
/// let mut items = ItemStream::new(&input).unwrap();
/// let mut item = items.next().unwrap().unwrap();
/// let args = MultiplicitySelector::<Vec<i32>>::default()
/// .parse_with(item.args_mut(), ItemArgumentParseable::from_args)
/// .unwrap();
/// assert_eq!(args, [12, 66]);
// When implementing this, update the documentation in the `ItemValueParseable` derive.
pub trait ArgumentSetMethods: Copy + Sized {
/// The output type: the type of the field in the Item struct.
/// This is *not* the type of an individual netdoc argument;
/// that is not explicitly represented in the trait.
/// Parse zero or more argument(s) into `Self::Field`.
fn parse_with<P>(self, args: &mut ArgumentStream<'_>, parser: P) -> Result<Self::Field, AE>
P: for<'s> Fn(&mut ArgumentStream<'s>) -> Result<Self::Each, AE>;
/// Check that the element type is an Argument
fn check_argument_value_parseable(self)
impl<T> ArgumentSetMethods for MultiplicitySelector<Vec<T>> {
P: for<'s> Fn(&mut ArgumentStream<'s>) -> Result<Self::Each, AE>,
let mut acc = vec![];
while args.something_to_yield() {
acc.push(parser(args)?);
Ok(acc)
impl<T: Ord> ArgumentSetMethods for MultiplicitySelector<BTreeSet<T>> {
let mut acc = BTreeSet::new();
if !acc.insert(parser(args)?) {
return Err(AE::Invalid);
impl<T> ArgumentSetMethods for MultiplicitySelector<Option<T>> {
if !args.something_to_yield() {
return Ok(None);
Ok(Some(parser(args)?))
impl<T> ArgumentSetMethods for &MultiplicitySelector<T> {
parser(args)
/// Method for handling some multiplicity of Objects
/// use tor_netdoc::parse2::multiplicity::{MultiplicitySelector, ObjectSetMethods as _};
/// use tor_netdoc::parse2::{ItemStream, ParseInput};
/// let doc = "intro-item\n-----BEGIN OBJECT-----\naGVsbG8=\n-----END OBJECT-----\n";
/// let selector = MultiplicitySelector::<Option<String>>::default();
/// let obj = item.object().map(|obj| {
/// let data = obj.decode_data().unwrap();
/// String::from_utf8(data)
/// }).transpose().unwrap();
/// let obj = selector.resolve_option(obj).unwrap();
/// assert_eq!(obj, Some("hello".to_owned()));
pub trait ObjectSetMethods: Copy + Sized {
fn resolve_option(self, found: Option<Self::Each>) -> Result<Self::Field, EP>;
/// If the contained type is `ItemObjectParseable`, call its `check_label`
fn check_label(self, label: &str) -> Result<(), EP>
Self::Each: ItemObjectParseable,
Self::Each::check_label(label)
/// Check that the contained type can be parsed as an object
fn check_object_parseable(self)
impl<T> ObjectSetMethods for MultiplicitySelector<Option<T>> {
fn resolve_option(self, found: Option<Self::Each>) -> Result<Self::Field, EP> {
Ok(found)
impl<T> ObjectSetMethods for &MultiplicitySelector<T> {
found.ok_or(EP::MissingObject)