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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214
#![warn(missing_docs)]
/*!
# An owning reference.
This crate provides the _owning reference_ types `OwningRef` and `OwningRefMut`
that enables it to bundle a reference together with the owner of the data it points to.
This allows moving and dropping of an `OwningRef` without needing to recreate the reference.
This can sometimes be useful because Rust borrowing rules normally prevent
moving a type that has been moved from. For example, this kind of code gets rejected:
```compile_fail,E0515
fn return_owned_and_referenced<'a>() -> (Vec<u8>, &'a [u8]) {
let v = vec![1, 2, 3, 4];
let s = &v[1..3];
(v, s)
}
```
Even though, from a memory-layout point of view, this can be entirely safe
if the new location of the vector still lives longer than the lifetime `'a`
of the reference because the backing allocation of the vector does not change.
This library enables this safe usage by keeping the owner and the reference
bundled together in a wrapper type that ensure that lifetime constraint:
```
# use rustc_data_structures::owning_ref::OwningRef;
# fn main() {
fn return_owned_and_referenced() -> OwningRef<Vec<u8>, [u8]> {
let v = vec![1, 2, 3, 4];
let or = OwningRef::new(v);
let or = or.map(|v| &v[1..3]);
or
}
# }
```
It works by requiring owner types to dereference to stable memory locations
and preventing mutable access to root containers, which in practice requires heap allocation
as provided by `Box<T>`, `Rc<T>`, etc.
Also provided are typedefs for common owner type combinations,
which allow for less verbose type signatures.
For example, `BoxRef<T>` instead of `OwningRef<Box<T>, T>`.
The crate also provides the more advanced `OwningHandle` type,
which allows more freedom in bundling a dependent handle object
along with the data it depends on, at the cost of some unsafe needed in the API.
See the documentation around `OwningHandle` for more details.
# Examples
## Basics
```
use rustc_data_structures::owning_ref::BoxRef;
fn main() {
// Create an array owned by a Box.
let arr = Box::new([1, 2, 3, 4]) as Box<[i32]>;
// Transfer into a BoxRef.
let arr: BoxRef<[i32]> = BoxRef::new(arr);
assert_eq!(&*arr, &[1, 2, 3, 4]);
// We can slice the array without losing ownership or changing type.
let arr: BoxRef<[i32]> = arr.map(|arr| &arr[1..3]);
assert_eq!(&*arr, &[2, 3]);
// Also works for Arc, Rc, String and Vec!
}
```
## Caching a reference to a struct field
```
use rustc_data_structures::owning_ref::BoxRef;
fn main() {
struct Foo {
tag: u32,
x: u16,
y: u16,
z: u16,
}
let foo = Foo { tag: 1, x: 100, y: 200, z: 300 };
let or = BoxRef::new(Box::new(foo)).map(|foo| {
match foo.tag {
0 => &foo.x,
1 => &foo.y,
2 => &foo.z,
_ => panic!(),
}
});
assert_eq!(*or, 200);
}
```
## Caching a reference to an entry in a vector
```
use rustc_data_structures::owning_ref::VecRef;
fn main() {
let v = VecRef::new(vec![1, 2, 3, 4, 5]).map(|v| &v[3]);
assert_eq!(*v, 4);
}
```
## Caching a subslice of a String
```
use rustc_data_structures::owning_ref::StringRef;
fn main() {
let s = StringRef::new("hello world".to_owned())
.map(|s| s.split(' ').nth(1).unwrap());
assert_eq!(&*s, "world");
}
```
## Reference counted slices that share ownership of the backing storage
```
use rustc_data_structures::owning_ref::RcRef;
use std::rc::Rc;
fn main() {
let rc: RcRef<[i32]> = RcRef::new(Rc::new([1, 2, 3, 4]) as Rc<[i32]>);
assert_eq!(&*rc, &[1, 2, 3, 4]);
let rc_a: RcRef<[i32]> = rc.clone().map(|s| &s[0..2]);
let rc_b = rc.clone().map(|s| &s[1..3]);
let rc_c = rc.clone().map(|s| &s[2..4]);
assert_eq!(&*rc_a, &[1, 2]);
assert_eq!(&*rc_b, &[2, 3]);
assert_eq!(&*rc_c, &[3, 4]);
let rc_c_a = rc_c.clone().map(|s| &s[1]);
assert_eq!(&*rc_c_a, &4);
}
```
## Atomic reference counted slices that share ownership of the backing storage
```
use rustc_data_structures::owning_ref::ArcRef;
use std::sync::Arc;
fn main() {
use std::thread;
fn par_sum(rc: ArcRef<[i32]>) -> i32 {
if rc.len() == 0 {
return 0;
} else if rc.len() == 1 {
return rc[0];
}
let mid = rc.len() / 2;
let left = rc.clone().map(|s| &s[..mid]);
let right = rc.map(|s| &s[mid..]);
let left = thread::spawn(move || par_sum(left));
let right = thread::spawn(move || par_sum(right));
left.join().unwrap() + right.join().unwrap()
}
let rc: Arc<[i32]> = Arc::new([1, 2, 3, 4]);
let rc: ArcRef<[i32]> = rc.into();
assert_eq!(par_sum(rc), 10);
}
```
## References into RAII locks
```
use rustc_data_structures::owning_ref::RefRef;
use std::cell::{RefCell, Ref};
fn main() {
let refcell = RefCell::new((1, 2, 3, 4));
// Also works with Mutex and RwLock
let refref = {
let refref = RefRef::new(refcell.borrow()).map(|x| &x.3);
assert_eq!(*refref, 4);
// We move the RAII lock and the reference to one of
// the subfields in the data it guards here:
refref
};
assert_eq!(*refref, 4);
drop(refref);
assert_eq!(*refcell.borrow(), (1, 2, 3, 4));
}
```
## Mutable reference
When the owned container implements `DerefMut`, it is also possible to make
a _mutable owning reference_. (e.g., with `Box`, `RefMut`, `MutexGuard`)
```
use rustc_data_structures::owning_ref::RefMutRefMut;
use std::cell::{RefCell, RefMut};
fn main() {
let refcell = RefCell::new((1, 2, 3, 4));
let mut refmut_refmut = {
let mut refmut_refmut = RefMutRefMut::new(refcell.borrow_mut()).map_mut(|x| &mut x.3);
assert_eq!(*refmut_refmut, 4);
*refmut_refmut *= 2;
refmut_refmut
};
assert_eq!(*refmut_refmut, 8);
*refmut_refmut *= 2;
drop(refmut_refmut);
assert_eq!(*refcell.borrow(), (1, 2, 3, 16));
}
```
*/
pub use stable_deref_trait::{
CloneStableDeref as CloneStableAddress, StableDeref as StableAddress,
};
use std::mem;
/// An owning reference.
///
/// This wraps an owner `O` and a reference `&T` pointing
/// at something reachable from `O::Target` while keeping
/// the ability to move `self` around.
///
/// The owner is usually a pointer that points at some base type.
///
/// For more details and examples, see the module and method docs.
pub struct OwningRef<O, T: ?Sized> {
owner: O,
reference: *const T,
}
/// An mutable owning reference.
///
/// This wraps an owner `O` and a reference `&mut T` pointing
/// at something reachable from `O::Target` while keeping
/// the ability to move `self` around.
///
/// The owner is usually a pointer that points at some base type.
///
/// For more details and examples, see the module and method docs.
pub struct OwningRefMut<O, T: ?Sized> {
owner: O,
reference: *mut T,
}
/// Helper trait for an erased concrete type an owner dereferences to.
/// This is used in form of a trait object for keeping
/// something around to (virtually) call the destructor.
pub trait Erased {}
impl<T> Erased for T {}
/// Helper trait for erasing the concrete type of what an owner dereferences to,
/// for example `Box<T> -> Box<Erased>`. This would be unneeded with
/// higher kinded types support in the language.
#[allow(unused_lifetimes)]
pub unsafe trait IntoErased<'a> {
/// Owner with the dereference type substituted to `Erased`.
type Erased;
/// Performs the type erasure.
fn into_erased(self) -> Self::Erased;
}
/// Helper trait for erasing the concrete type of what an owner dereferences to,
/// for example `Box<T> -> Box<Erased + Send>`. This would be unneeded with
/// higher kinded types support in the language.
#[allow(unused_lifetimes)]
pub unsafe trait IntoErasedSend<'a> {
/// Owner with the dereference type substituted to `Erased + Send`.
type Erased: Send;
/// Performs the type erasure.
fn into_erased_send(self) -> Self::Erased;
}
/// Helper trait for erasing the concrete type of what an owner dereferences to,
/// for example `Box<T> -> Box<Erased + Send + Sync>`. This would be unneeded with
/// higher kinded types support in the language.
#[allow(unused_lifetimes)]
pub unsafe trait IntoErasedSendSync<'a> {
/// Owner with the dereference type substituted to `Erased + Send + Sync`.
type Erased: Send + Sync;
/// Performs the type erasure.
fn into_erased_send_sync(self) -> Self::Erased;
}
/////////////////////////////////////////////////////////////////////////////
// OwningRef
/////////////////////////////////////////////////////////////////////////////
impl<O, T: ?Sized> OwningRef<O, T> {
/// Creates a new owning reference from an owner
/// initialized to the direct dereference of it.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::OwningRef;
///
/// fn main() {
/// let owning_ref = OwningRef::new(Box::new(42));
/// assert_eq!(*owning_ref, 42);
/// }
/// ```
pub fn new(o: O) -> Self
where
O: StableAddress,
O: Deref<Target = T>,
{
OwningRef { reference: &*o, owner: o }
}
/// Like `new`, but doesn’t require `O` to implement the `StableAddress` trait.
/// Instead, the caller is responsible to make the same promises as implementing the trait.
///
/// This is useful for cases where coherence rules prevents implementing the trait
/// without adding a dependency to this crate in a third-party library.
pub unsafe fn new_assert_stable_address(o: O) -> Self
where
O: Deref<Target = T>,
{
OwningRef { reference: &*o, owner: o }
}
/// Converts `self` into a new owning reference that points at something reachable
/// from the previous one.
///
/// This can be a reference to a field of `U`, something reachable from a field of
/// `U`, or even something unrelated with a `'static` lifetime.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::OwningRef;
///
/// fn main() {
/// let owning_ref = OwningRef::new(Box::new([1, 2, 3, 4]));
///
/// // create an owning reference that points at the
/// // third element of the array.
/// let owning_ref = owning_ref.map(|array| &array[2]);
/// assert_eq!(*owning_ref, 3);
/// }
/// ```
pub fn map<F, U: ?Sized>(self, f: F) -> OwningRef<O, U>
where
O: StableAddress,
F: FnOnce(&T) -> &U,
{
OwningRef { reference: f(&self), owner: self.owner }
}
/// Tries to convert `self` into a new owning reference that points
/// at something reachable from the previous one.
///
/// This can be a reference to a field of `U`, something reachable from a field of
/// `U`, or even something unrelated with a `'static` lifetime.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::OwningRef;
///
/// fn main() {
/// let owning_ref = OwningRef::new(Box::new([1, 2, 3, 4]));
///
/// // create an owning reference that points at the
/// // third element of the array.
/// let owning_ref = owning_ref.try_map(|array| {
/// if array[2] == 3 { Ok(&array[2]) } else { Err(()) }
/// });
/// assert_eq!(*owning_ref.unwrap(), 3);
/// }
/// ```
pub fn try_map<F, U: ?Sized, E>(self, f: F) -> Result<OwningRef<O, U>, E>
where
O: StableAddress,
F: FnOnce(&T) -> Result<&U, E>,
{
Ok(OwningRef { reference: f(&self)?, owner: self.owner })
}
/// Converts `self` into a new owning reference with a different owner type.
///
/// The new owner type needs to still contain the original owner in some way
/// so that the reference into it remains valid. This function is marked unsafe
/// because the user needs to manually uphold this guarantee.
pub unsafe fn map_owner<F, P>(self, f: F) -> OwningRef<P, T>
where
O: StableAddress,
P: StableAddress,
F: FnOnce(O) -> P,
{
OwningRef { reference: self.reference, owner: f(self.owner) }
}
/// Converts `self` into a new owning reference where the owner is wrapped
/// in an additional `Box<O>`.
///
/// This can be used to safely erase the owner of any `OwningRef<O, T>`
/// to an `OwningRef<Box<Erased>, T>`.
pub fn map_owner_box(self) -> OwningRef<Box<O>, T> {
OwningRef { reference: self.reference, owner: Box::new(self.owner) }
}
/// Erases the concrete base type of the owner with a trait object.
///
/// This allows mixing of owned references with different owner base types.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::{OwningRef, Erased};
///
/// fn main() {
/// // N.B., using the concrete types here for explicitness.
/// // For less verbose code type aliases like `BoxRef` are provided.
///
/// let owning_ref_a: OwningRef<Box<[i32; 4]>, [i32; 4]>
/// = OwningRef::new(Box::new([1, 2, 3, 4]));
///
/// let owning_ref_b: OwningRef<Box<Vec<(i32, bool)>>, Vec<(i32, bool)>>
/// = OwningRef::new(Box::new(vec![(0, false), (1, true)]));
///
/// let owning_ref_a: OwningRef<Box<[i32; 4]>, i32>
/// = owning_ref_a.map(|a| &a[0]);
///
/// let owning_ref_b: OwningRef<Box<Vec<(i32, bool)>>, i32>
/// = owning_ref_b.map(|a| &a[1].0);
///
/// let owning_refs: [OwningRef<Box<dyn Erased>, i32>; 2]
/// = [owning_ref_a.erase_owner(), owning_ref_b.erase_owner()];
///
/// assert_eq!(*owning_refs[0], 1);
/// assert_eq!(*owning_refs[1], 1);
/// }
/// ```
pub fn erase_owner<'a>(self) -> OwningRef<O::Erased, T>
where
O: IntoErased<'a>,
{
OwningRef { reference: self.reference, owner: self.owner.into_erased() }
}
/// Erases the concrete base type of the owner with a trait object which implements `Send`.
///
/// This allows mixing of owned references with different owner base types.
pub fn erase_send_owner<'a>(self) -> OwningRef<O::Erased, T>
where
O: IntoErasedSend<'a>,
{
OwningRef { reference: self.reference, owner: self.owner.into_erased_send() }
}
/// Erases the concrete base type of the owner with a trait object
/// which implements `Send` and `Sync`.
///
/// This allows mixing of owned references with different owner base types.
pub fn erase_send_sync_owner<'a>(self) -> OwningRef<O::Erased, T>
where
O: IntoErasedSendSync<'a>,
{
OwningRef { reference: self.reference, owner: self.owner.into_erased_send_sync() }
}
// UNIMPLEMENTED: wrap_owner
// FIXME: Naming convention?
/// A getter for the underlying owner.
pub fn owner(&self) -> &O {
&self.owner
}
// FIXME: Naming convention?
/// Discards the reference and retrieves the owner.
pub fn into_inner(self) -> O {
self.owner
}
}
impl<O, T: ?Sized> OwningRefMut<O, T> {
/// Creates a new owning reference from an owner
/// initialized to the direct dereference of it.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::OwningRefMut;
///
/// fn main() {
/// let owning_ref_mut = OwningRefMut::new(Box::new(42));
/// assert_eq!(*owning_ref_mut, 42);
/// }
/// ```
pub fn new(mut o: O) -> Self
where
O: StableAddress,
O: DerefMut<Target = T>,
{
OwningRefMut { reference: &mut *o, owner: o }
}
/// Like `new`, but doesn’t require `O` to implement the `StableAddress` trait.
/// Instead, the caller is responsible to make the same promises as implementing the trait.
///
/// This is useful for cases where coherence rules prevents implementing the trait
/// without adding a dependency to this crate in a third-party library.
pub unsafe fn new_assert_stable_address(mut o: O) -> Self
where
O: DerefMut<Target = T>,
{
OwningRefMut { reference: &mut *o, owner: o }
}
/// Converts `self` into a new _shared_ owning reference that points at
/// something reachable from the previous one.
///
/// This can be a reference to a field of `U`, something reachable from a field of
/// `U`, or even something unrelated with a `'static` lifetime.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::OwningRefMut;
///
/// fn main() {
/// let owning_ref_mut = OwningRefMut::new(Box::new([1, 2, 3, 4]));
///
/// // create an owning reference that points at the
/// // third element of the array.
/// let owning_ref = owning_ref_mut.map(|array| &array[2]);
/// assert_eq!(*owning_ref, 3);
/// }
/// ```
pub fn map<F, U: ?Sized>(mut self, f: F) -> OwningRef<O, U>
where
O: StableAddress,
F: FnOnce(&mut T) -> &U,
{
OwningRef { reference: f(&mut self), owner: self.owner }
}
/// Converts `self` into a new _mutable_ owning reference that points at
/// something reachable from the previous one.
///
/// This can be a reference to a field of `U`, something reachable from a field of
/// `U`, or even something unrelated with a `'static` lifetime.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::OwningRefMut;
///
/// fn main() {
/// let owning_ref_mut = OwningRefMut::new(Box::new([1, 2, 3, 4]));
///
/// // create an owning reference that points at the
/// // third element of the array.
/// let owning_ref_mut = owning_ref_mut.map_mut(|array| &mut array[2]);
/// assert_eq!(*owning_ref_mut, 3);
/// }
/// ```
pub fn map_mut<F, U: ?Sized>(mut self, f: F) -> OwningRefMut<O, U>
where
O: StableAddress,
F: FnOnce(&mut T) -> &mut U,
{
OwningRefMut { reference: f(&mut self), owner: self.owner }
}
/// Tries to convert `self` into a new _shared_ owning reference that points
/// at something reachable from the previous one.
///
/// This can be a reference to a field of `U`, something reachable from a field of
/// `U`, or even something unrelated with a `'static` lifetime.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::OwningRefMut;
///
/// fn main() {
/// let owning_ref_mut = OwningRefMut::new(Box::new([1, 2, 3, 4]));
///
/// // create an owning reference that points at the
/// // third element of the array.
/// let owning_ref = owning_ref_mut.try_map(|array| {
/// if array[2] == 3 { Ok(&array[2]) } else { Err(()) }
/// });
/// assert_eq!(*owning_ref.unwrap(), 3);
/// }
/// ```
pub fn try_map<F, U: ?Sized, E>(mut self, f: F) -> Result<OwningRef<O, U>, E>
where
O: StableAddress,
F: FnOnce(&mut T) -> Result<&U, E>,
{
Ok(OwningRef { reference: f(&mut self)?, owner: self.owner })
}
/// Tries to convert `self` into a new _mutable_ owning reference that points
/// at something reachable from the previous one.
///
/// This can be a reference to a field of `U`, something reachable from a field of
/// `U`, or even something unrelated with a `'static` lifetime.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::OwningRefMut;
///
/// fn main() {
/// let owning_ref_mut = OwningRefMut::new(Box::new([1, 2, 3, 4]));
///
/// // create an owning reference that points at the
/// // third element of the array.
/// let owning_ref_mut = owning_ref_mut.try_map_mut(|array| {
/// if array[2] == 3 { Ok(&mut array[2]) } else { Err(()) }
/// });
/// assert_eq!(*owning_ref_mut.unwrap(), 3);
/// }
/// ```
pub fn try_map_mut<F, U: ?Sized, E>(mut self, f: F) -> Result<OwningRefMut<O, U>, E>
where
O: StableAddress,
F: FnOnce(&mut T) -> Result<&mut U, E>,
{
Ok(OwningRefMut { reference: f(&mut self)?, owner: self.owner })
}
/// Converts `self` into a new owning reference with a different owner type.
///
/// The new owner type needs to still contain the original owner in some way
/// so that the reference into it remains valid. This function is marked unsafe
/// because the user needs to manually uphold this guarantee.
pub unsafe fn map_owner<F, P>(self, f: F) -> OwningRefMut<P, T>
where
O: StableAddress,
P: StableAddress,
F: FnOnce(O) -> P,
{
OwningRefMut { reference: self.reference, owner: f(self.owner) }
}
/// Converts `self` into a new owning reference where the owner is wrapped
/// in an additional `Box<O>`.
///
/// This can be used to safely erase the owner of any `OwningRefMut<O, T>`
/// to an `OwningRefMut<Box<Erased>, T>`.
pub fn map_owner_box(self) -> OwningRefMut<Box<O>, T> {
OwningRefMut { reference: self.reference, owner: Box::new(self.owner) }
}
/// Erases the concrete base type of the owner with a trait object.
///
/// This allows mixing of owned references with different owner base types.
///
/// # Example
/// ```
/// use rustc_data_structures::owning_ref::{OwningRefMut, Erased};
///
/// fn main() {
/// // N.B., using the concrete types here for explicitness.
/// // For less verbose code type aliases like `BoxRef` are provided.
///
/// let owning_ref_mut_a: OwningRefMut<Box<[i32; 4]>, [i32; 4]>
/// = OwningRefMut::new(Box::new([1, 2, 3, 4]));
///
/// let owning_ref_mut_b: OwningRefMut<Box<Vec<(i32, bool)>>, Vec<(i32, bool)>>
/// = OwningRefMut::new(Box::new(vec![(0, false), (1, true)]));
///
/// let owning_ref_mut_a: OwningRefMut<Box<[i32; 4]>, i32>
/// = owning_ref_mut_a.map_mut(|a| &mut a[0]);
///
/// let owning_ref_mut_b: OwningRefMut<Box<Vec<(i32, bool)>>, i32>
/// = owning_ref_mut_b.map_mut(|a| &mut a[1].0);
///
/// let owning_refs_mut: [OwningRefMut<Box<dyn Erased>, i32>; 2]
/// = [owning_ref_mut_a.erase_owner(), owning_ref_mut_b.erase_owner()];
///
/// assert_eq!(*owning_refs_mut[0], 1);
/// assert_eq!(*owning_refs_mut[1], 1);
/// }
/// ```
pub fn erase_owner<'a>(self) -> OwningRefMut<O::Erased, T>
where
O: IntoErased<'a>,
{
OwningRefMut { reference: self.reference, owner: self.owner.into_erased() }
}
// UNIMPLEMENTED: wrap_owner
// FIXME: Naming convention?
/// A getter for the underlying owner.
pub fn owner(&self) -> &O {
&self.owner
}
// FIXME: Naming convention?
/// Discards the reference and retrieves the owner.
pub fn into_inner(self) -> O {
self.owner
}
}
/////////////////////////////////////////////////////////////////////////////
// OwningHandle
/////////////////////////////////////////////////////////////////////////////
use std::ops::{Deref, DerefMut};
/// `OwningHandle` is a complement to `OwningRef`. Where `OwningRef` allows
/// consumers to pass around an owned object and a dependent reference,
/// `OwningHandle` contains an owned object and a dependent _object_.
///
/// `OwningHandle` can encapsulate a `RefMut` along with its associated
/// `RefCell`, or an `RwLockReadGuard` along with its associated `RwLock`.
/// However, the API is completely generic and there are no restrictions on
/// what types of owning and dependent objects may be used.
///
/// `OwningHandle` is created by passing an owner object (which dereferences
/// to a stable address) along with a callback which receives a pointer to
/// that stable location. The callback may then dereference the pointer and
/// mint a dependent object, with the guarantee that the returned object will
/// not outlive the referent of the pointer.
///
/// Since the callback needs to dereference a raw pointer, it requires `unsafe`
/// code. To avoid forcing this unsafety on most callers, the `ToHandle` trait is
/// implemented for common data structures. Types that implement `ToHandle` can
/// be wrapped into an `OwningHandle` without passing a callback.
pub struct OwningHandle<O, H>
where
O: StableAddress,
H: Deref,
{
handle: H,
_owner: O,
}
impl<O, H> Deref for OwningHandle<O, H>
where
O: StableAddress,
H: Deref,
{
type Target = H::Target;
fn deref(&self) -> &H::Target {
self.handle.deref()
}
}
unsafe impl<O, H> StableAddress for OwningHandle<O, H>
where
O: StableAddress,
H: StableAddress,
{
}
impl<O, H> DerefMut for OwningHandle<O, H>
where
O: StableAddress,
H: DerefMut,
{
fn deref_mut(&mut self) -> &mut H::Target {
self.handle.deref_mut()
}
}
/// Trait to implement the conversion of owner to handle for common types.
pub trait ToHandle {
/// The type of handle to be encapsulated by the OwningHandle.
type Handle: Deref;
/// Given an appropriately-long-lived pointer to ourselves, create a
/// handle to be encapsulated by the `OwningHandle`.
unsafe fn to_handle(x: *const Self) -> Self::Handle;
}
/// Trait to implement the conversion of owner to mutable handle for common types.
pub trait ToHandleMut {
/// The type of handle to be encapsulated by the OwningHandle.
type HandleMut: DerefMut;
/// Given an appropriately-long-lived pointer to ourselves, create a
/// mutable handle to be encapsulated by the `OwningHandle`.
unsafe fn to_handle_mut(x: *const Self) -> Self::HandleMut;
}
impl<O, H> OwningHandle<O, H>
where
O: StableAddress<Target: ToHandle<Handle = H>>,
H: Deref,
{
/// Creates a new `OwningHandle` for a type that implements `ToHandle`. For types
/// that don't implement `ToHandle`, callers may invoke `new_with_fn`, which accepts
/// a callback to perform the conversion.
pub fn new(o: O) -> Self {
OwningHandle::new_with_fn(o, |x| unsafe { O::Target::to_handle(x) })
}
}
impl<O, H> OwningHandle<O, H>
where
O: StableAddress<Target: ToHandleMut<HandleMut = H>>,
H: DerefMut,
{
/// Creates a new mutable `OwningHandle` for a type that implements `ToHandleMut`.
pub fn new_mut(o: O) -> Self {
OwningHandle::new_with_fn(o, |x| unsafe { O::Target::to_handle_mut(x) })
}
}
impl<O, H> OwningHandle<O, H>
where
O: StableAddress,
H: Deref,
{
/// Creates a new OwningHandle. The provided callback will be invoked with
/// a pointer to the object owned by `o`, and the returned value is stored
/// as the object to which this `OwningHandle` will forward `Deref` and
/// `DerefMut`.
pub fn new_with_fn<F>(o: O, f: F) -> Self
where
F: FnOnce(*const O::Target) -> H,
{
let h: H;
{
h = f(o.deref() as *const O::Target);
}
OwningHandle { handle: h, _owner: o }
}
/// Creates a new OwningHandle. The provided callback will be invoked with
/// a pointer to the object owned by `o`, and the returned value is stored
/// as the object to which this `OwningHandle` will forward `Deref` and
/// `DerefMut`.
pub fn try_new<F, E>(o: O, f: F) -> Result<Self, E>
where
F: FnOnce(*const O::Target) -> Result<H, E>,
{
let h: H;
{
h = f(o.deref() as *const O::Target)?;
}
Ok(OwningHandle { handle: h, _owner: o })
}
}
/////////////////////////////////////////////////////////////////////////////
// std traits
/////////////////////////////////////////////////////////////////////////////
use std::borrow::Borrow;
use std::cmp::{Eq, Ord, Ordering, PartialEq, PartialOrd};
use std::convert::From;
use std::fmt::{self, Debug};
use std::hash::{Hash, Hasher};
use std::marker::{Send, Sync};
impl<O, T: ?Sized> Deref for OwningRef<O, T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { &*self.reference }
}
}
impl<O, T: ?Sized> Deref for OwningRefMut<O, T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { &*self.reference }
}
}
impl<O, T: ?Sized> DerefMut for OwningRefMut<O, T> {
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut *self.reference }
}
}
unsafe impl<O, T: ?Sized> StableAddress for OwningRef<O, T> {}
impl<O, T: ?Sized> AsRef<T> for OwningRef<O, T> {
fn as_ref(&self) -> &T {
&*self
}
}
impl<O, T: ?Sized> AsRef<T> for OwningRefMut<O, T> {
fn as_ref(&self) -> &T {
&*self
}
}
impl<O, T: ?Sized> AsMut<T> for OwningRefMut<O, T> {
fn as_mut(&mut self) -> &mut T {
&mut *self
}
}
impl<O, T: ?Sized> Borrow<T> for OwningRef<O, T> {
fn borrow(&self) -> &T {
&*self
}
}
impl<O, T: ?Sized> From<O> for OwningRef<O, T>
where
O: StableAddress,
O: Deref<Target = T>,
{
fn from(owner: O) -> Self {
OwningRef::new(owner)
}
}
impl<O, T: ?Sized> From<O> for OwningRefMut<O, T>
where
O: StableAddress,
O: DerefMut<Target = T>,
{
fn from(owner: O) -> Self {
OwningRefMut::new(owner)
}
}
impl<O, T: ?Sized> From<OwningRefMut<O, T>> for OwningRef<O, T>
where
O: StableAddress,
O: DerefMut<Target = T>,
{
fn from(other: OwningRefMut<O, T>) -> Self {
OwningRef { owner: other.owner, reference: other.reference }
}
}
// ^ FIXME: Is an Into impl for calling into_inner() possible as well?
impl<O, T: ?Sized> Debug for OwningRef<O, T>
where
O: Debug,
T: Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "OwningRef {{ owner: {:?}, reference: {:?} }}", self.owner(), &**self)
}
}
impl<O, T: ?Sized> Debug for OwningRefMut<O, T>
where
O: Debug,
T: Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "OwningRefMut {{ owner: {:?}, reference: {:?} }}", self.owner(), &**self)
}
}
impl<O, T: ?Sized> Clone for OwningRef<O, T>
where
O: CloneStableAddress,
{
fn clone(&self) -> Self {
OwningRef { owner: self.owner.clone(), reference: self.reference }
}
}
unsafe impl<O, T: ?Sized> CloneStableAddress for OwningRef<O, T> where O: CloneStableAddress {}
unsafe impl<O, T: ?Sized> Send for OwningRef<O, T>
where
O: Send,
for<'a> &'a T: Send,
{
}
unsafe impl<O, T: ?Sized> Sync for OwningRef<O, T>
where
O: Sync,
for<'a> &'a T: Sync,
{
}
unsafe impl<O, T: ?Sized> Send for OwningRefMut<O, T>
where
O: Send,
for<'a> &'a mut T: Send,
{
}
unsafe impl<O, T: ?Sized> Sync for OwningRefMut<O, T>
where
O: Sync,
for<'a> &'a mut T: Sync,
{
}
impl Debug for dyn Erased {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "<Erased>",)
}
}
impl<O, T: ?Sized> PartialEq for OwningRef<O, T>
where
T: PartialEq,
{
fn eq(&self, other: &Self) -> bool {
(&*self as &T).eq(&*other as &T)
}
}
impl<O, T: ?Sized> Eq for OwningRef<O, T> where T: Eq {}
impl<O, T: ?Sized> PartialOrd for OwningRef<O, T>
where
T: PartialOrd,
{
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
(&*self as &T).partial_cmp(&*other as &T)
}
}
impl<O, T: ?Sized> Ord for OwningRef<O, T>
where
T: Ord,
{
fn cmp(&self, other: &Self) -> Ordering {
(&*self as &T).cmp(&*other as &T)
}
}
impl<O, T: ?Sized> Hash for OwningRef<O, T>
where
T: Hash,
{
fn hash<H: Hasher>(&self, state: &mut H) {
(&*self as &T).hash(state);
}
}
impl<O, T: ?Sized> PartialEq for OwningRefMut<O, T>
where
T: PartialEq,
{
fn eq(&self, other: &Self) -> bool {
(&*self as &T).eq(&*other as &T)
}
}
impl<O, T: ?Sized> Eq for OwningRefMut<O, T> where T: Eq {}
impl<O, T: ?Sized> PartialOrd for OwningRefMut<O, T>
where
T: PartialOrd,
{
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
(&*self as &T).partial_cmp(&*other as &T)
}
}
impl<O, T: ?Sized> Ord for OwningRefMut<O, T>
where
T: Ord,
{
fn cmp(&self, other: &Self) -> Ordering {
(&*self as &T).cmp(&*other as &T)
}
}
impl<O, T: ?Sized> Hash for OwningRefMut<O, T>
where
T: Hash,
{
fn hash<H: Hasher>(&self, state: &mut H) {
(&*self as &T).hash(state);
}
}
/////////////////////////////////////////////////////////////////////////////
// std types integration and convenience type defs
/////////////////////////////////////////////////////////////////////////////
use std::boxed::Box;
use std::cell::{Ref, RefCell, RefMut};
use std::rc::Rc;
use std::sync::Arc;
use std::sync::{MutexGuard, RwLockReadGuard, RwLockWriteGuard};
impl<T: 'static> ToHandle for RefCell<T> {
type Handle = Ref<'static, T>;
unsafe fn to_handle(x: *const Self) -> Self::Handle {
(*x).borrow()
}
}
impl<T: 'static> ToHandleMut for RefCell<T> {
type HandleMut = RefMut<'static, T>;
unsafe fn to_handle_mut(x: *const Self) -> Self::HandleMut {
(*x).borrow_mut()
}
}
// N.B., implementing ToHandle{,Mut} for Mutex and RwLock requires a decision
// about which handle creation to use (i.e., read() vs try_read()) as well as
// what to do with error results.
/// Typedef of an owning reference that uses a `Box` as the owner.
pub type BoxRef<T, U = T> = OwningRef<Box<T>, U>;
/// Typedef of an owning reference that uses a `Vec` as the owner.
pub type VecRef<T, U = T> = OwningRef<Vec<T>, U>;
/// Typedef of an owning reference that uses a `String` as the owner.
pub type StringRef = OwningRef<String, str>;
/// Typedef of an owning reference that uses an `Rc` as the owner.
pub type RcRef<T, U = T> = OwningRef<Rc<T>, U>;
/// Typedef of an owning reference that uses an `Arc` as the owner.
pub type ArcRef<T, U = T> = OwningRef<Arc<T>, U>;
/// Typedef of an owning reference that uses a `Ref` as the owner.
pub type RefRef<'a, T, U = T> = OwningRef<Ref<'a, T>, U>;
/// Typedef of an owning reference that uses a `RefMut` as the owner.
pub type RefMutRef<'a, T, U = T> = OwningRef<RefMut<'a, T>, U>;
/// Typedef of an owning reference that uses a `MutexGuard` as the owner.
pub type MutexGuardRef<'a, T, U = T> = OwningRef<MutexGuard<'a, T>, U>;
/// Typedef of an owning reference that uses an `RwLockReadGuard` as the owner.
pub type RwLockReadGuardRef<'a, T, U = T> = OwningRef<RwLockReadGuard<'a, T>, U>;
/// Typedef of an owning reference that uses an `RwLockWriteGuard` as the owner.
pub type RwLockWriteGuardRef<'a, T, U = T> = OwningRef<RwLockWriteGuard<'a, T>, U>;
/// Typedef of a mutable owning reference that uses a `Box` as the owner.
pub type BoxRefMut<T, U = T> = OwningRefMut<Box<T>, U>;
/// Typedef of a mutable owning reference that uses a `Vec` as the owner.
pub type VecRefMut<T, U = T> = OwningRefMut<Vec<T>, U>;
/// Typedef of a mutable owning reference that uses a `String` as the owner.
pub type StringRefMut = OwningRefMut<String, str>;
/// Typedef of a mutable owning reference that uses a `RefMut` as the owner.
pub type RefMutRefMut<'a, T, U = T> = OwningRefMut<RefMut<'a, T>, U>;
/// Typedef of a mutable owning reference that uses a `MutexGuard` as the owner.
pub type MutexGuardRefMut<'a, T, U = T> = OwningRefMut<MutexGuard<'a, T>, U>;
/// Typedef of a mutable owning reference that uses an `RwLockWriteGuard` as the owner.
pub type RwLockWriteGuardRefMut<'a, T, U = T> = OwningRef<RwLockWriteGuard<'a, T>, U>;
unsafe impl<'a, T: 'a> IntoErased<'a> for Box<T> {
type Erased = Box<dyn Erased + 'a>;
fn into_erased(self) -> Self::Erased {
self
}
}
unsafe impl<'a, T: 'a> IntoErased<'a> for Rc<T> {
type Erased = Rc<dyn Erased + 'a>;
fn into_erased(self) -> Self::Erased {
self
}
}
unsafe impl<'a, T: 'a> IntoErased<'a> for Arc<T> {
type Erased = Arc<dyn Erased + 'a>;
fn into_erased(self) -> Self::Erased {
self
}
}
unsafe impl<'a, T: Send + 'a> IntoErasedSend<'a> for Box<T> {
type Erased = Box<dyn Erased + Send + 'a>;
fn into_erased_send(self) -> Self::Erased {
self
}
}
unsafe impl<'a, T: Send + 'a> IntoErasedSendSync<'a> for Box<T> {
type Erased = Box<dyn Erased + Sync + Send + 'a>;
fn into_erased_send_sync(self) -> Self::Erased {
let result: Box<dyn Erased + Send + 'a> = self;
// This is safe since Erased can always implement Sync
// Only the destructor is available and it takes &mut self
unsafe { mem::transmute(result) }
}
}
unsafe impl<'a, T: Send + Sync + 'a> IntoErasedSendSync<'a> for Arc<T> {
type Erased = Arc<dyn Erased + Send + Sync + 'a>;
fn into_erased_send_sync(self) -> Self::Erased {
self
}
}
/// Typedef of an owning reference that uses an erased `Box` as the owner.
pub type ErasedBoxRef<U> = OwningRef<Box<dyn Erased>, U>;
/// Typedef of an owning reference that uses an erased `Rc` as the owner.
pub type ErasedRcRef<U> = OwningRef<Rc<dyn Erased>, U>;
/// Typedef of an owning reference that uses an erased `Arc` as the owner.
pub type ErasedArcRef<U> = OwningRef<Arc<dyn Erased>, U>;
/// Typedef of a mutable owning reference that uses an erased `Box` as the owner.
pub type ErasedBoxRefMut<U> = OwningRefMut<Box<dyn Erased>, U>;
#[cfg(test)]
mod tests;