1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538
#[cfg(any(feature="batch_ct", feature="batch_rt"))] use crate::batch::{ CpsBatch }; #[cfg(feature="batch_ct")] use crate::batch::{ new_batch_ct }; #[cfg(feature="batch_rt")] use crate::batch::{ new_batch_rt, FnBoxRt }; #[cfg(feature="detach")] mod detach; // detached paths #[cfg(feature="detach")] use detach::{ DetachedRoot }; #[cfg(feature="detach")] pub use detach::{ Attach, DetachedPath }; #[cfg(feature="traversal")] pub mod traversal; #[cfg(feature="traversal")] use traversal::{ Each, Of }; #[cfg(feature="batch_rt")] use alloc::vec::Vec; /// A smart access protocol. /// /// It is intended to be used through a [`Cps`](trait.Cps.html)-bounded type. pub trait At<Index> { type View: ?Sized; /// Accesses data at a specified index. /// /// If there is some data (or some bidirectional procedure) associated /// with the index then `access_at` must apply `f` to this data. /// /// If the transformation result can be placed back into `self` then /// it must be placed back and `access_at` must return `Some(f(data))`. /// /// Otherwise `None` __must__ be returned and `self` must stay unchanged. /// /// In essence `access_at` returns `None` if and only if `self` has /// not been touched. /// /// ### Note /// /// The following two cases are indistinguishable: /// /// * a view couldn't be obtained (and thus `f` had not been called) /// * `f` had been called but failed to mutate the view in a meaningful way /// /// If you need to distinguish between these cases you can use some side-effect of `f`. fn access_at<R, F>(&mut self, i: Index, f: F) -> Option<R> where F: FnOnce(&mut Self::View) -> R; } /// Anything that can provide (or refuse to provide) a mutable parameter /// for a function. /// /// You __do not need__ to implement `Cps` for anything: it's already implemented /// for [`AT`](struct.AT.html) and `&mut T`, and it's sufficient for almost all /// purposes. Implement [`At`](trait.At.html) instead. /// /// The main usecase for this trait is to be used as a bound on /// parameter and return types of functions: /// `Cps<View=T>`-bounded type can be thought of as a /// lifetimeless analogue of `&mut T`. /// /// In fact all default implementors of `Cps` have an internal lifetime /// parameter. If needed it can be exposed using `+ 'a` syntax in a trait /// bound, but in many cases one can do very well without any explicit lifetimes. pub trait Cps: Sized { type View: ?Sized; /// Returns `Some(f(..))` or `None`. /// /// The rules governing the value returned are defined by an implementation. fn access<R, F>(self, f: F) -> Option<R> where F: FnOnce(&mut Self::View) -> R; /// Equivalent to `self.access(|x| std::mem::replace(x, new_val))` fn replace(self, new_val: Self::View) -> Option<Self::View> where Self::View: Sized { self.access(|x| core::mem::replace(x, new_val)) } /// Equivalent to `self.access(|_| ())` fn touch(self) -> Option<()> where { self.access(|_| ()) } /// Equivalent to `self.access(|x| x.clone())` fn get_clone(self) -> Option<Self::View> where Self::View: Sized + Clone { self.access(|x| x.clone()) } /// “Moves in the direction” of the provided index. /// /// __Not intended for overriding.__ fn at<Index>(self, i: Index) -> AT<Self, ((), Index)> where Self::View: At<Index> { AT { cps: self, list: ((), i) } } #[cfg(feature="batch_ct")] /// Constructs a [compile-time batch](struct.CpsBatch.html). /// /// __Not intended for overriding.__ /// /// _Present only on `batch_ct`._ fn batch_ct(self) -> CpsBatch<Self, ()> { new_batch_ct(self) } #[cfg(feature="batch_rt")] /// Constructs a [runtime batch](struct.CpsBatch.html). /// /// __Not intended for overriding.__ /// /// _Present only on `batch_rt`._ fn batch_rt<R>(self) -> CpsBatch<Self, Vec<FnBoxRt<Self::View, R>>> { new_batch_rt(self) } #[cfg(feature="detach")] /// Attaches a [detached](trait.Attach.html) path. /// /// __Not intended for overriding.__ /// /// _Present only on `detach`._ fn attach<Path, V: ?Sized>(self, path: Path) -> AT<Self, Path::List> where Path: Attach<Self::View, View=V>, { path.attach_to(self) } #[cfg(feature="detach")] /// Creates a new detach point. /// /// __Not intended for overriding.__ /// /// _Present only on `detach`._ /// /// ### Usage example /// /// The [`.detach()`](struct.AT.html#method.detach) method /// detaches a part beginning at the closest detach point: /// /// ``` /// # use smart_access::Cps; /// let mut foo = Some(Some(1)); /// let mut bar = Some(2); /// /// // the detached part /// // /------\ /// let (left, right) = foo.at(()).cut().at(()).detach(); /// /// assert!(bar.attach(right).replace(3) == Some(2)); /// assert!(bar == Some(3)); /// /// assert!(left.at(()).replace(4) == Some(1)); /// assert!(foo == Some(Some(4))); /// ``` fn cut(self) -> AT<Self, ()> { AT { cps: self, list: () } } } /// `access` is guaranteed to return `Some(f(..))` impl<T: ?Sized> Cps for &mut T { type View = T; fn access<R, F>(self, f: F) -> Option<R> where F: FnOnce(&mut T) -> R { Some(f(self)) } } /// A “reference” to some “location”. /// /// With default [`Cps`](trait.Cps.html) implementations /// (and with the `detach` feature disabled) every `AT` is /// usually a “path component” list of type /// /// `AT<&mut root, (..((((), I1), I2), I3) .. In)>` /// /// But beware! Starting with the version `0.5` there is a possibility /// of accidentally creating multilevel hierarchies like /// /// `AT<AT<&mut root, ((), I1)>, ((), I2)>` /// /// by using the [`at` of `Cps`](trait.Cps.html#method.at) instead of /// its [`AT`-override](#method.at). /// /// Moreover, the `detach` feature is now based on such nonflat structures. /// /// ## Usage in function types /// /// Though `AT` is exposed, it's strongly recommended to use /// [`impl Cps<View=T>`](trait.Cps.html) as a return type of functions /// and [`Cps<View=T>`](trait.Cps.html) bounds on their parameters. /// /// But when needed (for example, due to some complex lifetimes), usage of `AT` /// can be facilitated by the [`path`](macro.path.html) macro allowing one /// to write /// /// `AT<CPS, path!(I, J, K)>` /// /// instead of /// /// `AT<CPS, ((((), I), J), K)>` /// /// ## Detaching paths /// /// Enabling `detach` feature allows one to [detach](#method.detach) `AT`s from their roots. /// /// Without this feature only a single component can be detached: /// /// ``` /// use smart_access::Cps; /// /// let mut foo = vec![vec![1,2], vec![3,4]]; /// /// let (foo_i, j) = foo.at(0).at(0).into(); /// assert!(foo_i.at(1).replace(5) == Some(2)); /// ``` /// /// ### Note /// /// _Relevant only with the `detach` feature enabled._ /// /// If you pass a detached path to a function then you should use /// a [`Path: Attach<CPS::View, View=V>`](trait.Attach.html) bound /// instead of a [`Cps<View=V>`](trait.Cps.html) bound. /// /// I.e. /// /// ``` /// # #[cfg(feature="detach")] fn test() { /// # use smart_access::{Cps, Attach, detached_at}; /// fn replace_at<CPS: Cps, Path, V>(cps: CPS, path: Path, x: V) -> Option<V> where /// Path: Attach<CPS::View, View=V>, /// { /// cps.attach(path).replace(x) /// } /// /// let mut vec = vec![1,2,3]; /// /// assert!(replace_at(&mut vec, detached_at(0), 4) == Some(1)); /// assert!(vec == vec![4,2,3]); /// # } /// # #[cfg(not(feature="detach"))] fn test() {} /// # test(); /// ``` /// /// But sometimes an explicit `AT` can be useful (the example below /// is artificial and thus not very illuminating...): /// /// ``` /// # #[cfg(feature="detach")] fn test() { /// use smart_access::*; /// /// fn get_ij<CPS, U, V, W>(a_i: AT<CPS, path!(usize)>, j: usize) /// -> impl Attach<W, View=V> where /// CPS: Cps<View=W>, /// W: At<usize, View=U> + ?Sized, /// U: At<usize, View=V> + ?Sized, /// V: ?Sized, /// { /// let (a,i) = a_i.into(); /// let (_, path) = a.at(i).at(j).detach(); /// /// path /// } /// /// let mut foo = vec![vec![1,2], vec![3,4]]; /// let path = get_ij(detached_at(1), 0); /// /// assert!(foo.attach(path).replace(5) == Some(3)); /// # } /// # #[cfg(not(feature="detach"))] fn test() {} /// # test(); /// ``` #[must_use] #[cfg_attr(feature="detach", derive(Clone))] #[derive(Debug)] pub struct AT<CPS, List> { cps: CPS, list: List, } /// `access` returns `Some` / `None` according to the rules described [here](trait.At.html) impl<CPS: Cps, Path> Cps for AT<CPS, Path> where Path: AtView<CPS::View> { type View = Path::View; fn access<R, F>(self, f: F) -> Option<R> where F: FnOnce(&mut Self::View) -> R { self.list.give_access(self.cps, f) } } impl<CPS, List> AT<CPS, List> { /// Override for [`at` of `Cps`](trait.Cps.html#method.at). /// /// Preserves flat structure. pub fn at<Index, View: ?Sized>(self, i: Index) -> AT<CPS, (List, Index)> where AT<CPS, List>: Cps<View=View>, View: At<Index> { AT { cps: self.cps, list: (self.list, i) } } /// Override for [`from` of `Each`](traversal/trait.Each.html#method.from). /// /// Preserves flat structure. #[cfg(feature="traversal")] pub fn from<Index, View: ?Sized>(self, i: Index) -> AT<CPS, (List, Index)> where AT<CPS, List>: Each<View=View>, View: Of<Index>, Index: Clone { AT { cps: self.cps, list: (self.list, i) } } } /// `AT` can be broken apart to detach a single path component. /// /// A more general attach/detach framework is accessible /// through the `detach` feature. impl<CPS,Prev,I> From<AT<CPS,(Prev,I)>> for (AT<CPS,Prev>,I) { fn from(at: AT<CPS,(Prev,I)>) -> Self { let (prev, index) = at.list; (AT { cps: at.cps, list: prev}, index) } } #[cfg(feature="detach")] impl<CPS: Cps, List> AT<CPS, List> { /// Detaches the path starting from the nearest [detach point](trait.Cps.html#method.cut). /// /// _Present only on `detach`._ /// /// ### Usage example /// /// ``` /// use smart_access::Cps; /// /// let mut foo = vec![vec![vec![0]]]; /// let mut bar = vec![vec![vec![0]]]; /// /// let (_, detached) = foo.at(0).at(0).at(0).detach(); /// /// // Detached paths are cloneable (if indices are cloneable) /// let the_same_path = detached.clone(); /// /// bar.attach(the_same_path).replace(1); /// assert!(foo == vec![vec![vec![0]]]); /// assert!(bar == vec![vec![vec![1]]]); /// /// foo.attach(detached).replace(2); /// assert!(foo == vec![vec![vec![2]]]); /// assert!(bar == vec![vec![vec![1]]]); /// /// let (_, path) = bar.at(0).at(0).detach(); /// bar.attach(path.at(0)).replace(3); /// assert!(bar == vec![vec![vec![3]]]); /// ``` pub fn detach(self) -> (CPS, DetachedPath<CPS::View, List>) { (self.cps, AT { cps: DetachedRoot::new(), list: self.list }) } } /// Creates a detached path. __Requires `detach` feature.__ /// /// The type of a value returned by `detached_at::<V, I>` /// implements [`Attach<V, View=<V as At<I>>::View>`](trait.Attach.html). /// /// _Present only on `detach`._ /// /// ### Usage example /// /// A simple case when detached paths could be helpful: creating /// a detached path and cloning it several times. /// /// ``` /// use smart_access::Cps; /// /// let reference_path = smart_access::detached_at(()).at(()).at(()); /// /// let mut items = vec![ Some(Some(Ok(1))), Some(None), Some(Some(Err(2))) ]; /// /// let sum = items.iter_mut().map(|wrapped| { /// wrapped.attach(reference_path.clone()) /// .access(|x| *x) /// .into_iter() /// .sum::<i32>() /// }).sum::<i32>(); /// /// assert!(sum == 1); /// ``` /// /// A more convoluted example: a functional index combinator. /// /// ``` /// use smart_access::{Attach, Cps}; /// /// type Mat = Vec<Vec<f64>>; /// /// fn mat_index(i: usize, j: usize) -> impl Attach<Mat, View=f64> { /// smart_access::detached_at(i).at(j) /// } /// /// let mut mat = vec![ /// vec![1., 2.], /// vec![3., 4.] /// ]; /// /// assert!(mat.attach(mat_index(1,1)).replace(0.) == Some(4.)); /// ``` /// /// But note that a more idiomatic approach would be /// /// ``` /// use smart_access::{Cps, At}; /// /// struct Mat { numbers: Vec<Vec<f64>> }; /// /// impl At<(usize, usize)> for Mat { /// type View = f64; /// /// fn access_at<R,F>(&mut self, ij: (usize, usize), f: F) -> Option<R> where /// F: FnOnce(&mut f64) -> R /// { /// let (i, j) = ij; /// /// self.numbers.at(i).at(j).access(f) /// } /// } /// /// let mut mat = Mat { numbers: vec![ /// vec![1., 2.], /// vec![3., 4.] /// ]}; /// /// assert!(mat.at( (1,1) ).replace(0.) == Some(4.)); /// ``` #[cfg(feature="detach")] pub fn detached_at<View: ?Sized, I>(i: I) -> DetachedPath<View, ((), I)> where View: At<I> { AT { cps: DetachedRoot::new(), list: ((), i), } } /// A trait which may be needed alongside [`Attach`](trait.Attach.html) bounds. /// /// __Update (v 0.5.0): seems to be not needed now!__ /// /// Essentially it's a type-level function mapping the `View` type of a /// `Cps`-bounded value `x` and a path type of the form `(..((), I1), .. In)` /// to the `View` type of the value /// /// `x.at(i1) .. .at(in)` /// /// Technically it's a workaround for the inability of the /// Rust compiler to reliably infer types in presence of /// flexible (as in Haskell's `FlexibleContexts`) recurrent contexts. pub trait AtView<View: ?Sized>: Sized { type View: ?Sized; fn give_access<CPS, R, F>(self, cps: CPS, f: F) -> Option<R> where CPS: Cps<View=View>, F: FnOnce(&mut Self::View) -> R; } impl<View: ?Sized> AtView<View> for () { type View = View; fn give_access<CPS, R, F>(self, cps: CPS, f: F) -> Option<R> where CPS: Cps<View=View>, F: FnOnce(&mut Self::View) -> R { cps.access(f) } } impl<View: ?Sized, Prev, Index> AtView<View> for (Prev, Index) where Prev: AtView<View>, Prev::View: At<Index> { type View = <Prev::View as At<Index>>::View; fn give_access<CPS, R, F>(self, cps: CPS, f: F) -> Option<R> where CPS: Cps<View=View>, F: FnOnce(&mut Self::View) -> R { let (prev, index) = self; prev.give_access(cps, |v| { v.access_at(index, f) }).flatten() } }