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//! Derivable references to arbitarily nested fields. //! //! This crate contains a basic implementation of 'keypaths', a mechanism //! for creating paths of references to the properties of objects that can //! be used to get and set their underlying values. //! //! The general idea and design is strongly influenced by keypaths in Swift. //! //! To work with keypaths, types must implement the [`Keyable`][] trait; in most //! cases this will be derived. //! //! [`KeyPath`][] instances can then be created with the [`keypath!`][] macro. //! //! # Examples //! //! ``` //! use keypath::{Keyable, KeyPath, keypath}; //! //! #[derive(Keyable)] //! struct Person { //! name: String, //! friends: Vec<String>, //! size: Size, //! } //! //! #[derive(Keyable)] //! struct Size { //! big: bool, //! heft: u8, //! } //! //! let mut person = Person { //! name: "coco".into(), //! friends: vec!["eli".into(), "nico".into(), "yaya".into()], //! size: Size { big: false, heft: 45 } //! }; //! //! let first_friend: KeyPath<Person, String> = keypath!(Person.friends[0]); //! let heft = keypath!(Person.size.heft); //! //! assert_eq!(person[&first_friend], "eli"); //! //! // mutation: //! person[&heft] = 101; //! assert_eq!(person.size.heft, 101); //! //! ``` mod error; mod impls; pub mod internals; pub use error::{FieldError, FieldErrorKind}; pub use keypath_proc_macros::{keypath, Keyable}; use std::any::Any; use std::borrow::Cow; use std::marker::PhantomData; /// A non-fallible keypath. pub struct KeyPath<Root: ?Sized, Value: 'static> { partial: PartialKeyPath<Root>, _value: PhantomData<Value>, } // we don't really use this yet #[doc(hidden)] /// A keypath for a known route, but which doesn't know the destination type. #[derive(Debug)] pub struct PartialKeyPath<Root: ?Sized> { fields: Cow<'static, [internals::PathComponent]>, _root: PhantomData<Root>, } impl<Root, Value> KeyPath<Root, Value> { /// Create a new typed `KeyPath` from the provided fields. /// /// This method does not ensure the path is valid; it is intended /// to be called after a path has been type-checked, presumably in the /// context of a proc_macro. #[doc(hidden)] pub const fn __conjure_from_abyss(fields: &'static [internals::PathComponent]) -> Self { KeyPath { partial: PartialKeyPath { fields: Cow::Borrowed(fields), _root: PhantomData, }, _value: PhantomData, } } /// Create a new `KeyPath` by combining two routes. /// /// The final type of the first route must be the first type of the second /// route; assuming both paths were created with the [`keypath!`] macro, /// the resulting path must be valid. /// /// # Examples /// /// ``` /// use keypath::{Keyable, KeyPath, keypath}; /// /// #[derive(Keyable)] /// struct Person { /// name: String, /// friends: Vec<String>, /// size: Size, /// } /// /// #[derive(Keyable)] /// struct Size { /// big: bool, /// heft: u8, /// } /// /// let mut person = Person { /// name: "coco".into(), /// friends: vec!["eli".into(), "nico".into(), "yaya".into()], /// size: Size { big: false, heft: 45 } /// }; /// /// let size = keypath!(Person.size); /// let heft = keypath!(Size.heft); /// let combined = size.append(&heft); /// /// assert_eq!(person[&combined], 45); /// ``` pub fn append<T>(&self, other: &KeyPath<Value, T>) -> KeyPath<Root, T> { let mut partial = self.partial.clone(); partial .fields .to_mut() .extend(other.partial.fields.iter().clone()); KeyPath { partial, _value: other._value, } } } /// A trait for types that can be indexed with keypaths. pub trait Keyable: internals::RawKeyable { /// A type that describes properties on the inner type, for compile-time checking. /// /// This is the worst part of the code right now? We generate structs with magic /// names for each Keyable type. type Mirror; /// Return an instance of this type's mirror. fn mirror() -> Self::Mirror; //TODO: this is a bit of a mess, and I don't know what methods we will want //or need. Having partial keypaths or keypaths that are failable seems reasonable, //but I don't know what the types are going to look like yet. /// Attempt to traverse a series of `PathComponent`s, returning an `&dyn Any` /// if successful. fn try_any_at_path( &self, path: impl AsRef<[internals::PathComponent]>, ) -> Result<&dyn Any, FieldError> { self.get_field(path.as_ref()) .map(internals::RawKeyable::as_any) } /// Attempt to traverse a series of `PathComponent`s, returning an `&mut dyn Any` /// if successful. fn try_any_at_path_mut( &mut self, path: impl AsRef<[internals::PathComponent]>, ) -> Result<&mut dyn Any, FieldError> { self.get_field_mut(path.as_ref()) .map(internals::RawKeyable::as_any_mut) } //NOTE: these two methods are intended in cases where the keypath has not been //validated, but currently we don't really support creating invalid keypaths. #[doc(hidden)] fn try_item_at_path<T>(&self, path: &KeyPath<Self, T>) -> Result<&T, FieldError> { self.try_any_at_path(path) ////FIXME: no unwrap here, some new more expresesive error type instead .map(|t| t.downcast_ref().unwrap()) } #[doc(hidden)] fn try_item_at_path_mut<T>(&mut self, path: &KeyPath<Self, T>) -> Result<&mut T, FieldError> { self.try_any_at_path_mut(path) //FIXME: no unwrap here, some new more expresesive error type instead .map(|t| t.downcast_mut().unwrap()) } /// Get a reference to the value at the provided path. /// /// You generally won't need to call this, since you can use `[index]` /// syntax instead. /// /// Assuming the path was constructed with the [`keypath!`] macro, this /// method will not fail. /// /// /// # Panics /// /// I lied, it will fail if you provide an index into a collection and /// that item does not exist. fn item_at_path<T>(&self, path: &KeyPath<Self, T>) -> &T { self.try_item_at_path(path).unwrap() } /// Get a mutable reference to the value at the provided path. /// /// You generally won't need to call this, since you can use `[index]` /// syntax instead. /// /// Assuming the path was constructed with the [`keypath!`] macro, this /// method will not fail. /// /// /// # Panics /// /// I lied, it will fail if you provide an index into a collection and /// that item does not exist. fn item_at_path_mut<T>(&mut self, path: &KeyPath<Self, T>) -> &mut T { self.try_item_at_path_mut(path).unwrap() } } impl<Root: ?Sized, Value: 'static> AsRef<[internals::PathComponent]> for KeyPath<Root, Value> { fn as_ref(&self) -> &[internals::PathComponent] { self.partial.fields.as_ref() } } impl<R: ?Sized> Clone for PartialKeyPath<R> { fn clone(&self) -> Self { PartialKeyPath { fields: self.fields.clone(), _root: PhantomData, } } }