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Diffstat (limited to 'library/core/src/any.rs')
| -rw-r--r-- | library/core/src/any.rs | 590 |
1 files changed, 0 insertions, 590 deletions
diff --git a/library/core/src/any.rs b/library/core/src/any.rs index 09f52d692..8f5404d97 100644 --- a/library/core/src/any.rs +++ b/library/core/src/any.rs @@ -83,72 +83,6 @@ //! } //! ``` //! -//! # `Provider` and `Demand` -//! -//! `Provider` and the associated APIs support generic, type-driven access to data, and a mechanism -//! for implementers to provide such data. The key parts of the interface are the `Provider` -//! trait for objects which can provide data, and the [`request_value`] and [`request_ref`] -//! functions for requesting data from an object which implements `Provider`. Generally, end users -//! should not call `request_*` directly, they are helper functions for intermediate implementers -//! to use to implement a user-facing interface. This is purely for the sake of ergonomics, there is -//! no safety concern here; intermediate implementers can typically support methods rather than -//! free functions and use more specific names. -//! -//! Typically, a data provider is a trait object of a trait which extends `Provider`. A user will -//! request data from a trait object by specifying the type of the data. -//! -//! ## Data flow -//! -//! * A user requests an object of a specific type, which is delegated to `request_value` or -//! `request_ref` -//! * `request_*` creates a `Demand` object and passes it to `Provider::provide` -//! * The data provider's implementation of `Provider::provide` tries providing values of -//! different types using `Demand::provide_*`. If the type matches the type requested by -//! the user, the value will be stored in the `Demand` object. -//! * `request_*` unpacks the `Demand` object and returns any stored value to the user. -//! -//! ## Examples -//! -//! ``` -//! # #![feature(provide_any)] -//! use std::any::{Provider, Demand, request_ref}; -//! -//! // Definition of MyTrait, a data provider. -//! trait MyTrait: Provider { -//! // ... -//! } -//! -//! // Methods on `MyTrait` trait objects. -//! impl dyn MyTrait + '_ { -//! /// Get a reference to a field of the implementing struct. -//! pub fn get_context_by_ref<T: ?Sized + 'static>(&self) -> Option<&T> { -//! request_ref::<T>(self) -//! } -//! } -//! -//! // Downstream implementation of `MyTrait` and `Provider`. -//! # struct SomeConcreteType { some_string: String } -//! impl MyTrait for SomeConcreteType { -//! // ... -//! } -//! -//! impl Provider for SomeConcreteType { -//! fn provide<'a>(&'a self, demand: &mut Demand<'a>) { -//! // Provide a string reference. We could provide multiple values with -//! // different types here. -//! demand.provide_ref::<String>(&self.some_string); -//! } -//! } -//! -//! // Downstream usage of `MyTrait`. -//! fn use_my_trait(obj: &dyn MyTrait) { -//! // Request a &String from obj. -//! let _ = obj.get_context_by_ref::<String>().unwrap(); -//! } -//! ``` -//! -//! In this example, if the concrete type of `obj` in `use_my_trait` is `SomeConcreteType`, then -//! the `get_context_by_ref` call will return a reference to `obj.some_string` with type `&String`. #![stable(feature = "rust1", since = "1.0.0")] @@ -697,9 +631,6 @@ impl TypeId { #[stable(feature = "rust1", since = "1.0.0")] #[rustc_const_unstable(feature = "const_type_id", issue = "77125")] pub const fn of<T: ?Sized + 'static>() -> TypeId { - #[cfg(bootstrap)] - let t = intrinsics::type_id::<T>() as u128; - #[cfg(not(bootstrap))] let t: u128 = intrinsics::type_id::<T>(); TypeId { t } } @@ -801,524 +732,3 @@ pub const fn type_name<T: ?Sized>() -> &'static str { pub const fn type_name_of_val<T: ?Sized>(_val: &T) -> &'static str { type_name::<T>() } - -/////////////////////////////////////////////////////////////////////////////// -// Provider trait -/////////////////////////////////////////////////////////////////////////////// - -/// Trait implemented by a type which can dynamically provide values based on type. -#[unstable(feature = "provide_any", issue = "96024")] -pub trait Provider { - /// Data providers should implement this method to provide *all* values they are able to - /// provide by using `demand`. - /// - /// Note that the `provide_*` methods on `Demand` have short-circuit semantics: if an earlier - /// method has successfully provided a value, then later methods will not get an opportunity to - /// provide. - /// - /// # Examples - /// - /// Provides a reference to a field with type `String` as a `&str`, and a value of - /// type `i32`. - /// - /// ```rust - /// # #![feature(provide_any)] - /// use std::any::{Provider, Demand}; - /// # struct SomeConcreteType { field: String, num_field: i32 } - /// - /// impl Provider for SomeConcreteType { - /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { - /// demand.provide_ref::<str>(&self.field) - /// .provide_value::<i32>(self.num_field); - /// } - /// } - /// ``` - #[unstable(feature = "provide_any", issue = "96024")] - fn provide<'a>(&'a self, demand: &mut Demand<'a>); -} - -/// Request a value from the `Provider`. -/// -/// # Examples -/// -/// Get a string value from a provider. -/// -/// ```rust -/// # #![feature(provide_any)] -/// use std::any::{Provider, request_value}; -/// -/// fn get_string(provider: &impl Provider) -> String { -/// request_value::<String>(provider).unwrap() -/// } -/// ``` -#[unstable(feature = "provide_any", issue = "96024")] -pub fn request_value<'a, T>(provider: &'a (impl Provider + ?Sized)) -> Option<T> -where - T: 'static, -{ - request_by_type_tag::<'a, tags::Value<T>>(provider) -} - -/// Request a reference from the `Provider`. -/// -/// # Examples -/// -/// Get a string reference from a provider. -/// -/// ```rust -/// # #![feature(provide_any)] -/// use std::any::{Provider, request_ref}; -/// -/// fn get_str(provider: &impl Provider) -> &str { -/// request_ref::<str>(provider).unwrap() -/// } -/// ``` -#[unstable(feature = "provide_any", issue = "96024")] -pub fn request_ref<'a, T>(provider: &'a (impl Provider + ?Sized)) -> Option<&'a T> -where - T: 'static + ?Sized, -{ - request_by_type_tag::<'a, tags::Ref<tags::MaybeSizedValue<T>>>(provider) -} - -/// Request a specific value by tag from the `Provider`. -fn request_by_type_tag<'a, I>(provider: &'a (impl Provider + ?Sized)) -> Option<I::Reified> -where - I: tags::Type<'a>, -{ - let mut tagged = TaggedOption::<'a, I>(None); - provider.provide(tagged.as_demand()); - tagged.0 -} - -/////////////////////////////////////////////////////////////////////////////// -// Demand and its methods -/////////////////////////////////////////////////////////////////////////////// - -/// A helper object for providing data by type. -/// -/// A data provider provides values by calling this type's provide methods. -#[unstable(feature = "provide_any", issue = "96024")] -#[cfg_attr(not(doc), repr(transparent))] // work around https://github.com/rust-lang/rust/issues/90435 -pub struct Demand<'a>(dyn Erased<'a> + 'a); - -impl<'a> Demand<'a> { - /// Create a new `&mut Demand` from a `&mut dyn Erased` trait object. - fn new<'b>(erased: &'b mut (dyn Erased<'a> + 'a)) -> &'b mut Demand<'a> { - // SAFETY: transmuting `&mut (dyn Erased<'a> + 'a)` to `&mut Demand<'a>` is safe since - // `Demand` is repr(transparent). - unsafe { &mut *(erased as *mut dyn Erased<'a> as *mut Demand<'a>) } - } - - /// Provide a value or other type with only static lifetimes. - /// - /// # Examples - /// - /// Provides an `u8`. - /// - /// ```rust - /// #![feature(provide_any)] - /// - /// use std::any::{Provider, Demand}; - /// # struct SomeConcreteType { field: u8 } - /// - /// impl Provider for SomeConcreteType { - /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { - /// demand.provide_value::<u8>(self.field); - /// } - /// } - /// ``` - #[unstable(feature = "provide_any", issue = "96024")] - pub fn provide_value<T>(&mut self, value: T) -> &mut Self - where - T: 'static, - { - self.provide::<tags::Value<T>>(value) - } - - /// Provide a value or other type with only static lifetimes computed using a closure. - /// - /// # Examples - /// - /// Provides a `String` by cloning. - /// - /// ```rust - /// #![feature(provide_any)] - /// - /// use std::any::{Provider, Demand}; - /// # struct SomeConcreteType { field: String } - /// - /// impl Provider for SomeConcreteType { - /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { - /// demand.provide_value_with::<String>(|| self.field.clone()); - /// } - /// } - /// ``` - #[unstable(feature = "provide_any", issue = "96024")] - pub fn provide_value_with<T>(&mut self, fulfil: impl FnOnce() -> T) -> &mut Self - where - T: 'static, - { - self.provide_with::<tags::Value<T>>(fulfil) - } - - /// Provide a reference. The referee type must be bounded by `'static`, - /// but may be unsized. - /// - /// # Examples - /// - /// Provides a reference to a field as a `&str`. - /// - /// ```rust - /// #![feature(provide_any)] - /// - /// use std::any::{Provider, Demand}; - /// # struct SomeConcreteType { field: String } - /// - /// impl Provider for SomeConcreteType { - /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { - /// demand.provide_ref::<str>(&self.field); - /// } - /// } - /// ``` - #[unstable(feature = "provide_any", issue = "96024")] - pub fn provide_ref<T: ?Sized + 'static>(&mut self, value: &'a T) -> &mut Self { - self.provide::<tags::Ref<tags::MaybeSizedValue<T>>>(value) - } - - /// Provide a reference computed using a closure. The referee type - /// must be bounded by `'static`, but may be unsized. - /// - /// # Examples - /// - /// Provides a reference to a field as a `&str`. - /// - /// ```rust - /// #![feature(provide_any)] - /// - /// use std::any::{Provider, Demand}; - /// # struct SomeConcreteType { business: String, party: String } - /// # fn today_is_a_weekday() -> bool { true } - /// - /// impl Provider for SomeConcreteType { - /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { - /// demand.provide_ref_with::<str>(|| { - /// if today_is_a_weekday() { - /// &self.business - /// } else { - /// &self.party - /// } - /// }); - /// } - /// } - /// ``` - #[unstable(feature = "provide_any", issue = "96024")] - pub fn provide_ref_with<T: ?Sized + 'static>( - &mut self, - fulfil: impl FnOnce() -> &'a T, - ) -> &mut Self { - self.provide_with::<tags::Ref<tags::MaybeSizedValue<T>>>(fulfil) - } - - /// Provide a value with the given `Type` tag. - fn provide<I>(&mut self, value: I::Reified) -> &mut Self - where - I: tags::Type<'a>, - { - if let Some(res @ TaggedOption(None)) = self.0.downcast_mut::<I>() { - res.0 = Some(value); - } - self - } - - /// Provide a value with the given `Type` tag, using a closure to prevent unnecessary work. - fn provide_with<I>(&mut self, fulfil: impl FnOnce() -> I::Reified) -> &mut Self - where - I: tags::Type<'a>, - { - if let Some(res @ TaggedOption(None)) = self.0.downcast_mut::<I>() { - res.0 = Some(fulfil()); - } - self - } - - /// Check if the `Demand` would be satisfied if provided with a - /// value of the specified type. If the type does not match or has - /// already been provided, returns false. - /// - /// # Examples - /// - /// Check if an `u8` still needs to be provided and then provides - /// it. - /// - /// ```rust - /// #![feature(provide_any)] - /// - /// use std::any::{Provider, Demand}; - /// - /// struct Parent(Option<u8>); - /// - /// impl Provider for Parent { - /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { - /// if let Some(v) = self.0 { - /// demand.provide_value::<u8>(v); - /// } - /// } - /// } - /// - /// struct Child { - /// parent: Parent, - /// } - /// - /// impl Child { - /// // Pretend that this takes a lot of resources to evaluate. - /// fn an_expensive_computation(&self) -> Option<u8> { - /// Some(99) - /// } - /// } - /// - /// impl Provider for Child { - /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { - /// // In general, we don't know if this call will provide - /// // an `u8` value or not... - /// self.parent.provide(demand); - /// - /// // ...so we check to see if the `u8` is needed before - /// // we run our expensive computation. - /// if demand.would_be_satisfied_by_value_of::<u8>() { - /// if let Some(v) = self.an_expensive_computation() { - /// demand.provide_value::<u8>(v); - /// } - /// } - /// - /// // The demand will be satisfied now, regardless of if - /// // the parent provided the value or we did. - /// assert!(!demand.would_be_satisfied_by_value_of::<u8>()); - /// } - /// } - /// - /// let parent = Parent(Some(42)); - /// let child = Child { parent }; - /// assert_eq!(Some(42), std::any::request_value::<u8>(&child)); - /// - /// let parent = Parent(None); - /// let child = Child { parent }; - /// assert_eq!(Some(99), std::any::request_value::<u8>(&child)); - /// ``` - #[unstable(feature = "provide_any", issue = "96024")] - pub fn would_be_satisfied_by_value_of<T>(&self) -> bool - where - T: 'static, - { - self.would_be_satisfied_by::<tags::Value<T>>() - } - - /// Check if the `Demand` would be satisfied if provided with a - /// reference to a value of the specified type. If the type does - /// not match or has already been provided, returns false. - /// - /// # Examples - /// - /// Check if a `&str` still needs to be provided and then provides - /// it. - /// - /// ```rust - /// #![feature(provide_any)] - /// - /// use std::any::{Provider, Demand}; - /// - /// struct Parent(Option<String>); - /// - /// impl Provider for Parent { - /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { - /// if let Some(v) = &self.0 { - /// demand.provide_ref::<str>(v); - /// } - /// } - /// } - /// - /// struct Child { - /// parent: Parent, - /// name: String, - /// } - /// - /// impl Child { - /// // Pretend that this takes a lot of resources to evaluate. - /// fn an_expensive_computation(&self) -> Option<&str> { - /// Some(&self.name) - /// } - /// } - /// - /// impl Provider for Child { - /// fn provide<'a>(&'a self, demand: &mut Demand<'a>) { - /// // In general, we don't know if this call will provide - /// // a `str` reference or not... - /// self.parent.provide(demand); - /// - /// // ...so we check to see if the `&str` is needed before - /// // we run our expensive computation. - /// if demand.would_be_satisfied_by_ref_of::<str>() { - /// if let Some(v) = self.an_expensive_computation() { - /// demand.provide_ref::<str>(v); - /// } - /// } - /// - /// // The demand will be satisfied now, regardless of if - /// // the parent provided the reference or we did. - /// assert!(!demand.would_be_satisfied_by_ref_of::<str>()); - /// } - /// } - /// - /// let parent = Parent(Some("parent".into())); - /// let child = Child { parent, name: "child".into() }; - /// assert_eq!(Some("parent"), std::any::request_ref::<str>(&child)); - /// - /// let parent = Parent(None); - /// let child = Child { parent, name: "child".into() }; - /// assert_eq!(Some("child"), std::any::request_ref::<str>(&child)); - /// ``` - #[unstable(feature = "provide_any", issue = "96024")] - pub fn would_be_satisfied_by_ref_of<T>(&self) -> bool - where - T: ?Sized + 'static, - { - self.would_be_satisfied_by::<tags::Ref<tags::MaybeSizedValue<T>>>() - } - - fn would_be_satisfied_by<I>(&self) -> bool - where - I: tags::Type<'a>, - { - matches!(self.0.downcast::<I>(), Some(TaggedOption(None))) - } -} - -#[unstable(feature = "provide_any", issue = "96024")] -impl<'a> fmt::Debug for Demand<'a> { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.debug_struct("Demand").finish_non_exhaustive() - } -} - -/////////////////////////////////////////////////////////////////////////////// -// Type tags -/////////////////////////////////////////////////////////////////////////////// - -mod tags { - //! Type tags are used to identify a type using a separate value. This module includes type tags - //! for some very common types. - //! - //! Currently type tags are not exposed to the user. But in the future, if you want to use the - //! Provider API with more complex types (typically those including lifetime parameters), you - //! will need to write your own tags. - - use crate::marker::PhantomData; - - /// This trait is implemented by specific tag types in order to allow - /// describing a type which can be requested for a given lifetime `'a`. - /// - /// A few example implementations for type-driven tags can be found in this - /// module, although crates may also implement their own tags for more - /// complex types with internal lifetimes. - pub trait Type<'a>: Sized + 'static { - /// The type of values which may be tagged by this tag for the given - /// lifetime. - type Reified: 'a; - } - - /// Similar to the [`Type`] trait, but represents a type which may be unsized (i.e., has a - /// `?Sized` bound). E.g., `str`. - pub trait MaybeSizedType<'a>: Sized + 'static { - type Reified: 'a + ?Sized; - } - - impl<'a, T: Type<'a>> MaybeSizedType<'a> for T { - type Reified = T::Reified; - } - - /// Type-based tag for types bounded by `'static`, i.e., with no borrowed elements. - #[derive(Debug)] - pub struct Value<T: 'static>(PhantomData<T>); - - impl<'a, T: 'static> Type<'a> for Value<T> { - type Reified = T; - } - - /// Type-based tag similar to [`Value`] but which may be unsized (i.e., has a `?Sized` bound). - #[derive(Debug)] - pub struct MaybeSizedValue<T: ?Sized + 'static>(PhantomData<T>); - - impl<'a, T: ?Sized + 'static> MaybeSizedType<'a> for MaybeSizedValue<T> { - type Reified = T; - } - - /// Type-based tag for reference types (`&'a T`, where T is represented by - /// `<I as MaybeSizedType<'a>>::Reified`. - #[derive(Debug)] - pub struct Ref<I>(PhantomData<I>); - - impl<'a, I: MaybeSizedType<'a>> Type<'a> for Ref<I> { - type Reified = &'a I::Reified; - } -} - -/// An `Option` with a type tag `I`. -/// -/// Since this struct implements `Erased`, the type can be erased to make a dynamically typed -/// option. The type can be checked dynamically using `Erased::tag_id` and since this is statically -/// checked for the concrete type, there is some degree of type safety. -#[repr(transparent)] -struct TaggedOption<'a, I: tags::Type<'a>>(Option<I::Reified>); - -impl<'a, I: tags::Type<'a>> TaggedOption<'a, I> { - fn as_demand(&mut self) -> &mut Demand<'a> { - Demand::new(self as &mut (dyn Erased<'a> + 'a)) - } -} - -/// Represents a type-erased but identifiable object. -/// -/// This trait is exclusively implemented by the `TaggedOption` type. -unsafe trait Erased<'a>: 'a { - /// The `TypeId` of the erased type. - fn tag_id(&self) -> TypeId; -} - -unsafe impl<'a, I: tags::Type<'a>> Erased<'a> for TaggedOption<'a, I> { - fn tag_id(&self) -> TypeId { - TypeId::of::<I>() - } -} - -#[unstable(feature = "provide_any", issue = "96024")] -impl<'a> dyn Erased<'a> + 'a { - /// Returns some reference to the dynamic value if it is tagged with `I`, - /// or `None` otherwise. - #[inline] - fn downcast<I>(&self) -> Option<&TaggedOption<'a, I>> - where - I: tags::Type<'a>, - { - if self.tag_id() == TypeId::of::<I>() { - // SAFETY: Just checked whether we're pointing to an I. - Some(unsafe { &*(self as *const Self).cast::<TaggedOption<'a, I>>() }) - } else { - None - } - } - - /// Returns some mutable reference to the dynamic value if it is tagged with `I`, - /// or `None` otherwise. - #[inline] - fn downcast_mut<I>(&mut self) -> Option<&mut TaggedOption<'a, I>> - where - I: tags::Type<'a>, - { - if self.tag_id() == TypeId::of::<I>() { - // SAFETY: Just checked whether we're pointing to an I. - Some(unsafe { &mut *(self as *mut Self).cast::<TaggedOption<'a, I>>() }) - } else { - None - } - } -} |