├── .gitignore ├── Cargo.toml ├── LICENSE-APACHE ├── LICENSE-MIT ├── README.md └── src └── lib.rs /.gitignore: -------------------------------------------------------------------------------- 1 | /target 2 | Cargo.lock 3 | -------------------------------------------------------------------------------- /Cargo.toml: -------------------------------------------------------------------------------- 1 | [package] 2 | name = "object-provider" 3 | version = "0.2.0" 4 | authors = ["Nika Layzell "] 5 | edition = "2018" 6 | description = "Trait for requesting values by type from a given object" 7 | repository = "https://github.com/mystor/object-provider" 8 | license = "MIT OR Apache-2.0" 9 | 10 | [dependencies] 11 | -------------------------------------------------------------------------------- /LICENSE-APACHE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. 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See the documentation for more details. 8 | 9 | [`ObjectProvider`]: https://docs.rs/object-provider/latest/object_provider/trait.ObjectProvider.html 10 | -------------------------------------------------------------------------------- /src/lib.rs: -------------------------------------------------------------------------------- 1 | #![cfg_attr(not(test), no_std)] 2 | //! Trait for requesting values by type from a given object. 3 | //! 4 | //! # Examples 5 | //! 6 | //! ## Using a Provider 7 | //! 8 | //! ``` 9 | //! # use object_provider::*; 10 | //! # use std::path::{Path, PathBuf}; 11 | //! # use std::fmt::Debug; 12 | //! # use std::pin::Pin; 13 | //! # struct MyProvider { 14 | //! # path: PathBuf, 15 | //! # } 16 | //! # impl ObjectProvider for MyProvider { 17 | //! # fn provide<'a>(&'a self, request: Pin<&mut Request<'a>>) { 18 | //! # request 19 | //! # .provide_ref::(&self.path) 20 | //! # .provide_ref::(&self.path) 21 | //! # .provide_ref::(&self.path); 22 | //! # } 23 | //! # } 24 | //! # let my_path = Path::new("hello/world"); 25 | //! # let my_provider = MyProvider { path: my_path.to_owned() }; 26 | //! let provider: &dyn ObjectProvider; 27 | //! # provider = &my_provider; 28 | //! 29 | //! // It's possible to request concrete types like `PathBuf` 30 | //! let path_buf = provider.request_ref::().unwrap(); 31 | //! assert_eq!(path_buf, my_path); 32 | //! 33 | //! // Requesting `!Sized` types, like slices and trait objects, is also supported. 34 | //! let path = provider.request_ref::().unwrap(); 35 | //! assert_eq!(path, my_path); 36 | //! 37 | //! let debug = provider.request_ref::().unwrap(); 38 | //! assert_eq!( 39 | //! format!("{:?}", debug), 40 | //! format!("{:?}", my_path), 41 | //! ); 42 | //! 43 | //! // Types or interfaces not explicitly provided return `None`. 44 | //! assert!(provider.request_ref::().is_none()); 45 | //! assert!(provider.request_ref::>().is_none()); 46 | //! ``` 47 | //! 48 | //! ## Implementing a Provider 49 | //! 50 | //! ``` 51 | //! # use object_provider::*; 52 | //! # use std::path::{Path, PathBuf}; 53 | //! # use std::fmt::Debug; 54 | //! # use std::pin::Pin; 55 | //! struct MyProvider { 56 | //! path: PathBuf, 57 | //! } 58 | //! 59 | //! impl ObjectProvider for MyProvider { 60 | //! fn provide<'a>(&'a self, request: Pin<&mut Request<'a>>) { 61 | //! request 62 | //! .provide_ref::(&self.path) 63 | //! .provide_ref::(&self.path) 64 | //! .provide_ref::(&self.path); 65 | //! } 66 | //! } 67 | //! ``` 68 | 69 | use core::any::TypeId; 70 | use core::fmt; 71 | use core::marker::{PhantomData, PhantomPinned}; 72 | use core::pin::Pin; 73 | 74 | struct ReqRef(&'static T); 75 | struct ReqVal(T); 76 | 77 | /// A dynamic request for an object based on its type. 78 | #[repr(C)] 79 | pub struct Request<'a> { 80 | type_id: TypeId, 81 | _pinned: PhantomPinned, 82 | _marker: PhantomData<&'a ()>, 83 | } 84 | 85 | impl<'a> Request<'a> { 86 | /// Provides a reference of type `&'a T` in response to this request. 87 | /// 88 | /// If a reference of type `&'a T` has already been provided for this 89 | /// request, the existing value will be replaced by the newly provided 90 | /// value. 91 | /// 92 | /// This method can be chained within `provide` implementations to concisely 93 | /// provide multiple objects. 94 | pub fn provide_ref(self: Pin<&mut Self>, value: &'a T) -> Pin<&mut Self> { 95 | self.provide_ref_with(|| value) 96 | } 97 | 98 | /// Lazily provides a reference of type `&'a T` in response to this request. 99 | /// 100 | /// If a reference of type `&'a T` has already been provided for this 101 | /// request, the existing value will be replaced by the newly provided 102 | /// value. 103 | /// 104 | /// The passed closure is only called if the value will be successfully 105 | /// provided. 106 | /// 107 | /// This method can be chained within `provide` implementations to concisely 108 | /// provide multiple objects. 109 | pub fn provide_ref_with( 110 | mut self: Pin<&mut Self>, 111 | cb: F, 112 | ) -> Pin<&mut Self> 113 | where 114 | F: FnOnce() -> &'a T, 115 | { 116 | if self.is_ref::() { 117 | // safety: `self.is_ref::()` ensured the data field is `&'a T`. 118 | unsafe { 119 | *self.as_mut().downcast_unchecked::<&'a T>() = Some(cb()); 120 | } 121 | } 122 | self 123 | } 124 | 125 | /// Provides an value of type `T` in response to this request. 126 | /// 127 | /// If a value of type `T` has already been provided for this request, the 128 | /// existing value will be replaced by the newly provided value. 129 | /// 130 | /// This method can be chained within `provide` implementations to concisely 131 | /// provide multiple objects. 132 | pub fn provide_value(self: Pin<&mut Self>, value: T) -> Pin<&mut Self> { 133 | self.provide_value_with(|| value) 134 | } 135 | 136 | /// Lazily provides a value of type `T` in response to this request. 137 | /// 138 | /// If a value of type `T` has already been provided for this request, the 139 | /// existing value will be replaced by the newly provided value. 140 | /// 141 | /// The passed closure is only called if the value will be successfully 142 | /// provided. 143 | /// 144 | /// This method can be chained within `provide` implementations to concisely 145 | /// provide multiple objects. 146 | pub fn provide_value_with(mut self: Pin<&mut Self>, cb: F) -> Pin<&mut Self> 147 | where 148 | F: FnOnce() -> T, 149 | { 150 | if self.is_value::() { 151 | // safety: `self.is_value::()` ensured the data field is `T`. 152 | unsafe { 153 | *self.as_mut().downcast_unchecked::() = Some(cb()); 154 | } 155 | } 156 | self 157 | } 158 | 159 | /// Returns `true` if the requested type is `&'a T` 160 | pub fn is_ref(&self) -> bool { 161 | self.type_id == TypeId::of::>() 162 | } 163 | 164 | /// Returns `true` if the requested type is `T` 165 | pub fn is_value(&self) -> bool { 166 | self.type_id == TypeId::of::>() 167 | } 168 | 169 | // internal implementation detail - performs an unchecked downcast. 170 | unsafe fn downcast_unchecked(self: Pin<&mut Self>) -> &mut Option { 171 | let ptr = self.get_unchecked_mut() as *mut Self as *mut RequestBuf<'a, T>; 172 | &mut (*ptr).value 173 | } 174 | 175 | /// Calls the provided closure with a request for the the type `&'a T`, 176 | /// returning `Some(&T)` if the request was fulfilled, and `None` otherwise. 177 | /// 178 | /// The `ObjectProviderExt` trait provides helper methods specifically for 179 | /// types implementing `ObjectProvider`. 180 | pub fn request_ref(f: F) -> Option<&'a T> 181 | where 182 | F: FnOnce(Pin<&mut Request<'a>>), 183 | { 184 | let mut buf = RequestBuf::for_ref(); 185 | // safety: We never move `buf` after creating `pinned`. 186 | let mut pinned = unsafe { Pin::new_unchecked(&mut buf) }; 187 | f(pinned.as_mut().request()); 188 | pinned.take() 189 | } 190 | 191 | /// Calls the provided closure with a request for the the type `T`, 192 | /// returning `Some(T)` if the request was fulfilled, and `None` otherwise. 193 | /// 194 | /// The `ObjectProviderExt` trait provides helper methods specifically for 195 | /// types implementing `ObjectProvider`. 196 | pub fn request_value(f: F) -> Option 197 | where 198 | F: FnOnce(Pin<&mut Request<'a>>), 199 | { 200 | let mut buf = RequestBuf::for_value(); 201 | // safety: We never move `buf` after creating `pinned`. 202 | let mut pinned = unsafe { Pin::new_unchecked(&mut buf) }; 203 | f(pinned.as_mut().request()); 204 | pinned.take() 205 | } 206 | } 207 | 208 | impl<'a> fmt::Debug for Request<'a> { 209 | fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { 210 | f.debug_struct("Request") 211 | .field("type_id", &self.type_id) 212 | .finish() 213 | } 214 | } 215 | 216 | /// Low level buffer API used to create typed object requests. 217 | /// 218 | /// Due to a heavy dependency on [`Pin`], this type is inconvenient to use 219 | /// directly. Prefer using the [`ObjectProviderExt`] trait and [`Request::with`] 220 | /// APIs when possible. 221 | // Needs to have a known layout so we can do unsafe pointer shenanigans. 222 | #[repr(C)] 223 | #[derive(Debug)] 224 | struct RequestBuf<'a, T> { 225 | request: Request<'a>, 226 | value: Option, 227 | } 228 | 229 | impl<'a, T: ?Sized + 'static> RequestBuf<'a, &'a T> { 230 | /// Create a new `RequestBuf` object. 231 | /// 232 | /// This type must be pinned before it can be used. 233 | fn for_ref() -> Self { 234 | // safety: ReqRef is a marker type for `&'a T` 235 | unsafe { Self::new_internal(TypeId::of::>()) } 236 | } 237 | } 238 | 239 | impl<'a, T: 'static> RequestBuf<'a, T> { 240 | /// Create a new `RequestBuf` object. 241 | /// 242 | /// This type must be pinned before it can be used. 243 | fn for_value() -> Self { 244 | // safety: ReqVal is a marker type for `T` 245 | unsafe { Self::new_internal(TypeId::of::>()) } 246 | } 247 | } 248 | 249 | impl<'a, T> RequestBuf<'a, T> { 250 | unsafe fn new_internal(type_id: TypeId) -> Self { 251 | RequestBuf { 252 | request: Request { 253 | type_id, 254 | _pinned: PhantomPinned, 255 | _marker: PhantomData, 256 | }, 257 | value: None, 258 | } 259 | } 260 | 261 | /// Get the untyped `Request` reference for this `RequestBuf`. 262 | fn request(self: Pin<&mut Self>) -> Pin<&mut Request<'a>> { 263 | // safety: projecting Pin onto our `request` field. 264 | unsafe { self.map_unchecked_mut(|this| &mut this.request) } 265 | } 266 | 267 | /// Take a value previously provided to this `RequestBuf`. 268 | fn take(self: Pin<&mut Self>) -> Option { 269 | // safety: we don't project Pin onto our `value` field. 270 | unsafe { self.get_unchecked_mut().value.take() } 271 | } 272 | } 273 | 274 | /// Trait to provide other objects based on a requested type at runtime. 275 | /// 276 | /// See also the [`ObjectProviderExt`] trait which provides the `request` method. 277 | pub trait ObjectProvider { 278 | /// Provide an object of a given type in response to an untyped request. 279 | fn provide<'a>(&'a self, request: Pin<&mut Request<'a>>); 280 | } 281 | 282 | /// Methods supported by all [`ObjectProvider`] implementors. 283 | pub trait ObjectProviderExt { 284 | /// Request a reference of type `&T` from an object provider. 285 | fn request_ref(&self) -> Option<&T>; 286 | 287 | /// Request an owned value of type `T` from an object provider. 288 | fn request_value(&self) -> Option; 289 | } 290 | 291 | impl ObjectProviderExt for O { 292 | fn request_ref(&self) -> Option<&T> { 293 | Request::request_ref::(|req| self.provide(req)) 294 | } 295 | 296 | fn request_value(&self) -> Option { 297 | Request::request_value::(|req| self.provide(req)) 298 | } 299 | } 300 | 301 | #[cfg(test)] 302 | mod test { 303 | use super::*; 304 | use std::path::{Path, PathBuf}; 305 | 306 | #[test] 307 | fn basic_context() { 308 | struct HasContext { 309 | int: i32, 310 | path: PathBuf, 311 | } 312 | impl ObjectProvider for HasContext { 313 | fn provide<'a>(&'a self, request: Pin<&mut Request<'a>>) { 314 | request 315 | .provide_ref::(&self.int) 316 | .provide_ref::(&self.path) 317 | .provide_ref::(&self.int) 318 | .provide_value::(self.int); 319 | } 320 | } 321 | 322 | let provider: &dyn ObjectProvider = &HasContext { 323 | int: 10, 324 | path: PathBuf::new(), 325 | }; 326 | 327 | assert_eq!(provider.request_ref::(), Some(&10)); 328 | assert_eq!(provider.request_value::(), Some(10)); 329 | assert!(provider.request_ref::().is_none()); 330 | assert_eq!( 331 | provider 332 | .request_ref::() 333 | .map(|d| d.to_string()), 334 | Some("10".to_owned()) 335 | ); 336 | assert!(provider.request_ref::().is_none()); 337 | assert_eq!(provider.request_ref::(), Some(Path::new(""))); 338 | } 339 | } 340 | --------------------------------------------------------------------------------