cell/cell.rs
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
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Modified work Copyright 2018-2019 Daniel Mueller (deso@posteo.net).
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use std::cell::Cell;
use std::cell::UnsafeCell;
use std::cmp::Ordering;
use std::fmt;
use std::fmt::Debug;
use std::fmt::Display;
use std::mem;
use std::ops::Deref;
use std::ops::DerefMut;
/// A mutable memory location with dynamically checked borrow rules
///
/// See the [module-level documentation](index.html) for more.
pub struct RefCell<T: ?Sized> {
borrow: Cell<BorrowFlag>,
value: UnsafeCell<T>,
}
/// An error returned by [`RefCell::try_borrow`](struct.RefCell.html#method.try_borrow).
pub struct BorrowError {
_private: (),
}
impl Debug for BorrowError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("BorrowError").finish()
}
}
impl Display for BorrowError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Display::fmt("already mutably borrowed", f)
}
}
/// An error returned by [`RefCell::try_borrow_mut`](struct.RefCell.html#method.try_borrow_mut).
pub struct BorrowMutError {
_private: (),
}
impl Debug for BorrowMutError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("BorrowMutError").finish()
}
}
impl Display for BorrowMutError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
Display::fmt("already borrowed", f)
}
}
// Positive values represent the number of `Ref` active. Negative values
// represent the number of `RefMut` active. Multiple `RefMut`s can only be
// active at a time if they refer to distinct, nonoverlapping components of a
// `RefCell` (e.g., different ranges of a slice).
//
// `Ref` and `RefMut` are both two words in size, and so there will likely never
// be enough `Ref`s or `RefMut`s in existence to overflow half of the `usize`
// range. Thus, a `BorrowFlag` will probably never overflow or underflow.
// However, this is not a guarantee, as a pathological program could repeatedly
// create and then mem::forget `Ref`s or `RefMut`s. Thus, all code must
// explicitly check for overflow and underflow in order to avoid unsafety, or at
// least behave correctly in the event that overflow or underflow happens (e.g.,
// see BorrowRef::new).
type BorrowFlag = isize;
const UNUSED: BorrowFlag = 0;
#[inline(always)]
fn is_writing(x: BorrowFlag) -> bool {
x < UNUSED
}
#[inline(always)]
fn is_reading(x: BorrowFlag) -> bool {
x > UNUSED
}
impl<T> RefCell<T> {
/// Creates a new `RefCell` containing `value`.
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
///
/// let c = RefCell::new(5);
/// ```
#[inline]
pub const fn new(value: T) -> RefCell<T> {
RefCell {
value: UnsafeCell::new(value),
borrow: Cell::new(UNUSED),
}
}
/// Consumes the `RefCell`, returning the wrapped value.
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
///
/// let c = RefCell::new(5);
///
/// let five = c.into_inner();
/// ```
#[inline]
pub fn into_inner(self) -> T {
// Since this function takes `self` (the `RefCell`) by value, the
// compiler statically verifies that it is not currently borrowed.
// Therefore the following assertion is just a `debug_assert!`.
debug_assert!(self.borrow.get() == UNUSED);
self.value.into_inner()
}
/// Replaces the wrapped value with a new one, returning the old value,
/// without deinitializing either one.
///
/// This function corresponds to [`std::mem::replace`](../mem/fn.replace.html).
///
/// # Panics
///
/// Panics if the value is currently borrowed.
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
/// let cell = RefCell::new(5);
/// let old_value = cell.replace(6);
/// assert_eq!(old_value, 5);
/// assert_eq!(cell, RefCell::new(6));
/// ```
#[inline]
pub fn replace(&self, t: T) -> T {
mem::replace(&mut *self.borrow_mut(), t)
}
/// Replaces the wrapped value with a new one computed from `f`, returning
/// the old value, without deinitializing either one.
///
/// # Panics
///
/// Panics if the value is currently borrowed.
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
/// let cell = RefCell::new(5);
/// let old_value = cell.replace_with(|&mut old| old + 1);
/// assert_eq!(old_value, 5);
/// assert_eq!(cell, RefCell::new(6));
/// ```
#[inline]
pub fn replace_with<F: FnOnce(&mut T) -> T>(&self, f: F) -> T {
let mut_borrow = &mut *self.borrow_mut();
let replacement = f(mut_borrow);
mem::replace(mut_borrow, replacement)
}
/// Swaps the wrapped value of `self` with the wrapped value of `other`,
/// without deinitializing either one.
///
/// This function corresponds to [`std::mem::swap`](../mem/fn.swap.html).
///
/// # Panics
///
/// Panics if the value in either `RefCell` is currently borrowed.
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
/// let c = RefCell::new(5);
/// let d = RefCell::new(6);
/// c.swap(&d);
/// assert_eq!(c, RefCell::new(6));
/// assert_eq!(d, RefCell::new(5));
/// ```
#[inline]
pub fn swap(&self, other: &Self) {
mem::swap(&mut *self.borrow_mut(), &mut *other.borrow_mut())
}
}
impl<T: ?Sized> RefCell<T> {
/// Immutably borrows the wrapped value.
///
/// The borrow lasts until the returned `Ref` exits scope. Multiple
/// immutable borrows can be taken out at the same time.
///
/// # Panics
///
/// Panics if the value is currently mutably borrowed. For a non-panicking variant, use
/// [`try_borrow`](#method.try_borrow).
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
///
/// let c = RefCell::new(5);
///
/// let borrowed_five = c.borrow();
/// let borrowed_five2 = c.borrow();
/// ```
///
/// An example of panic:
///
/// ```
/// use std::cell::RefCell;
/// use std::thread;
///
/// let result = thread::spawn(move || {
/// let c = RefCell::new(5);
/// let m = c.borrow_mut();
///
/// let b = c.borrow(); // this causes a panic
/// }).join();
///
/// assert!(result.is_err());
/// ```
#[inline]
pub fn borrow(&self) -> Ref<T> {
self.try_borrow().expect("already mutably borrowed")
}
/// Immutably borrows the wrapped value, returning an error if the value is currently mutably
/// borrowed.
///
/// The borrow lasts until the returned `Ref` exits scope. Multiple immutable borrows can be
/// taken out at the same time.
///
/// This is the non-panicking variant of [`borrow`](#method.borrow).
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
///
/// let c = RefCell::new(5);
///
/// {
/// let m = c.borrow_mut();
/// assert!(c.try_borrow().is_err());
/// }
///
/// {
/// let m = c.borrow();
/// assert!(c.try_borrow().is_ok());
/// }
/// ```
#[inline]
pub fn try_borrow(&self) -> Result<Ref<T>, BorrowError> {
match BorrowRef::new(&self.borrow) {
Some(b) => Ok(Ref {
value: unsafe { &*self.value.get() },
borrow: b,
}),
None => Err(BorrowError { _private: () }),
}
}
/// Mutably borrows the wrapped value.
///
/// The borrow lasts until the returned `RefMut` or all `RefMut`s derived
/// from it exit scope. The value cannot be borrowed while this borrow is
/// active.
///
/// # Panics
///
/// Panics if the value is currently borrowed. For a non-panicking variant, use
/// [`try_borrow_mut`](#method.try_borrow_mut).
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
///
/// let c = RefCell::new(5);
///
/// *c.borrow_mut() = 7;
///
/// assert_eq!(*c.borrow(), 7);
/// ```
///
/// An example of panic:
///
/// ```
/// use std::cell::RefCell;
/// use std::thread;
///
/// let result = thread::spawn(move || {
/// let c = RefCell::new(5);
/// let m = c.borrow();
///
/// let b = c.borrow_mut(); // this causes a panic
/// }).join();
///
/// assert!(result.is_err());
/// ```
#[inline]
pub fn borrow_mut(&self) -> RefMut<T> {
self.try_borrow_mut().expect("already borrowed")
}
/// Mutably borrows the wrapped value, returning an error if the value is currently borrowed.
///
/// The borrow lasts until the returned `RefMut` or all `RefMut`s derived
/// from it exit scope. The value cannot be borrowed while this borrow is
/// active.
///
/// This is the non-panicking variant of [`borrow_mut`](#method.borrow_mut).
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
///
/// let c = RefCell::new(5);
///
/// {
/// let m = c.borrow();
/// assert!(c.try_borrow_mut().is_err());
/// }
///
/// assert!(c.try_borrow_mut().is_ok());
/// ```
#[inline]
pub fn try_borrow_mut(&self) -> Result<RefMut<T>, BorrowMutError> {
match BorrowRefMut::new(&self.borrow) {
Some(b) => Ok(RefMut {
value: unsafe { &mut *self.value.get() },
borrow: b,
}),
None => Err(BorrowMutError { _private: () }),
}
}
/// Returns a raw pointer to the underlying data in this cell.
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
///
/// let c = RefCell::new(5);
///
/// let ptr = c.as_ptr();
/// ```
#[inline]
pub fn as_ptr(&self) -> *mut T {
self.value.get()
}
/// Returns a mutable reference to the underlying data.
///
/// This call borrows `RefCell` mutably (at compile-time) so there is no
/// need for dynamic checks.
///
/// However be cautious: this method expects `self` to be mutable, which is
/// generally not the case when using a `RefCell`. Take a look at the
/// [`borrow_mut`] method instead if `self` isn't mutable.
///
/// Also, please be aware that this method is only for special circumstances and is usually
/// not what you want. In case of doubt, use [`borrow_mut`] instead.
///
/// [`borrow_mut`]: #method.borrow_mut
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
///
/// let mut c = RefCell::new(5);
/// *c.get_mut() += 1;
///
/// assert_eq!(c, RefCell::new(6));
/// ```
#[inline]
pub fn get_mut(&mut self) -> &mut T {
unsafe {
&mut *self.value.get()
}
}
}
unsafe impl<T: ?Sized> Send for RefCell<T> where T: Send {}
// Note that `RefCell` does not explicitly have a negative trait bound
// for `Sync` as negative trait bounds are only available on nightly but
// we want to be available on stable. However, `RefCell` still won't
// implement `Sync` as it contains an `std::cell::UnsafeCell` which has
// such a negative trait bound for `Sync`.
impl<T: Clone> Clone for RefCell<T> {
/// # Panics
///
/// Panics if the value is currently mutably borrowed.
#[inline]
fn clone(&self) -> RefCell<T> {
RefCell::new(self.borrow().clone())
}
}
impl<T:Default> Default for RefCell<T> {
/// Creates a `RefCell<T>`, with the `Default` value for T.
#[inline]
fn default() -> RefCell<T> {
RefCell::new(Default::default())
}
}
impl<T: ?Sized + PartialEq> PartialEq for RefCell<T> {
/// # Panics
///
/// Panics if the value in either `RefCell` is currently borrowed.
#[inline]
fn eq(&self, other: &RefCell<T>) -> bool {
*self.borrow() == *other.borrow()
}
}
impl<T: ?Sized + Eq> Eq for RefCell<T> {}
impl<T: ?Sized + PartialOrd> PartialOrd for RefCell<T> {
/// # Panics
///
/// Panics if the value in either `RefCell` is currently borrowed.
#[inline]
fn partial_cmp(&self, other: &RefCell<T>) -> Option<Ordering> {
self.borrow().partial_cmp(&*other.borrow())
}
/// # Panics
///
/// Panics if the value in either `RefCell` is currently borrowed.
#[inline]
fn lt(&self, other: &RefCell<T>) -> bool {
*self.borrow() < *other.borrow()
}
/// # Panics
///
/// Panics if the value in either `RefCell` is currently borrowed.
#[inline]
fn le(&self, other: &RefCell<T>) -> bool {
*self.borrow() <= *other.borrow()
}
/// # Panics
///
/// Panics if the value in either `RefCell` is currently borrowed.
#[inline]
fn gt(&self, other: &RefCell<T>) -> bool {
*self.borrow() > *other.borrow()
}
/// # Panics
///
/// Panics if the value in either `RefCell` is currently borrowed.
#[inline]
fn ge(&self, other: &RefCell<T>) -> bool {
*self.borrow() >= *other.borrow()
}
}
impl<T: ?Sized + Ord> Ord for RefCell<T> {
/// # Panics
///
/// Panics if the value in either `RefCell` is currently borrowed.
#[inline]
fn cmp(&self, other: &RefCell<T>) -> Ordering {
self.borrow().cmp(&*other.borrow())
}
}
impl<T> From<T> for RefCell<T> {
fn from(t: T) -> RefCell<T> {
RefCell::new(t)
}
}
struct BorrowRef<'b> {
borrow: &'b Cell<BorrowFlag>,
}
impl<'b> BorrowRef<'b> {
#[inline]
fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRef<'b>> {
let b = borrow.get();
if is_writing(b) || b == isize::max_value() {
// If there's currently a writing borrow, or if incrementing the
// refcount would overflow into a writing borrow.
None
} else {
borrow.set(b + 1);
Some(BorrowRef { borrow })
}
}
}
impl Drop for BorrowRef<'_> {
#[inline]
fn drop(&mut self) {
let borrow = self.borrow.get();
debug_assert!(is_reading(borrow));
self.borrow.set(borrow - 1);
}
}
impl Clone for BorrowRef<'_> {
#[inline]
fn clone(&self) -> Self {
// Since this Ref exists, we know the borrow flag
// is a reading borrow.
let borrow = self.borrow.get();
debug_assert!(is_reading(borrow));
// Prevent the borrow counter from overflowing into
// a writing borrow.
assert!(borrow != isize::max_value());
self.borrow.set(borrow + 1);
BorrowRef { borrow: self.borrow }
}
}
/// Wraps a borrowed reference to a value in a `RefCell` box.
/// A wrapper type for an immutably borrowed value from a `RefCell<T>`.
///
/// See the [module-level documentation](index.html) for more.
pub struct Ref<'b, T: ?Sized + 'b> {
value: &'b T,
borrow: BorrowRef<'b>,
}
impl<T: ?Sized> Deref for Ref<'_, T> {
type Target = T;
#[inline]
fn deref(&self) -> &T {
self.value
}
}
impl<'b, T: ?Sized> Ref<'b, T> {
/// Copies a `Ref`.
///
/// The `RefCell` is already immutably borrowed, so this cannot fail.
///
/// This is an associated function that needs to be used as
/// `Ref::clone(...)`. A `Clone` implementation or a method would interfere
/// with the widespread use of `r.borrow().clone()` to clone the contents of
/// a `RefCell`.
#[inline]
pub fn clone(orig: &Ref<'b, T>) -> Ref<'b, T> {
Ref {
value: orig.value,
borrow: orig.borrow.clone(),
}
}
/// Makes a new `Ref` for a component of the borrowed data.
///
/// The `RefCell` is already immutably borrowed, so this cannot fail.
///
/// This is an associated function that needs to be used as `Ref::map(...)`.
/// A method would interfere with methods of the same name on the contents
/// of a `RefCell` used through `Deref`.
///
/// # Examples
///
/// ```
/// use std::cell::{RefCell, Ref};
///
/// let c = RefCell::new((5, 'b'));
/// let b1: Ref<(u32, char)> = c.borrow();
/// let b2: Ref<u32> = Ref::map(b1, |t| &t.0);
/// assert_eq!(*b2, 5)
/// ```
#[inline]
pub fn map<U: ?Sized, F>(orig: Ref<'b, T>, f: F) -> Ref<'b, U>
where F: FnOnce(&T) -> &U
{
Ref {
value: f(orig.value),
borrow: orig.borrow,
}
}
/// Splits a `Ref` into multiple `Ref`s for different components of the
/// borrowed data.
///
/// The `RefCell` is already immutably borrowed, so this cannot fail.
///
/// This is an associated function that needs to be used as
/// `Ref::map_split(...)`. A method would interfere with methods of the same
/// name on the contents of a `RefCell` used through `Deref`.
///
/// # Examples
///
/// ```
/// use std::cell::{Ref, RefCell};
///
/// let cell = RefCell::new([1, 2, 3, 4]);
/// let borrow = cell.borrow();
/// let (begin, end) = Ref::map_split(borrow, |slice| slice.split_at(2));
/// assert_eq!(*begin, [1, 2]);
/// assert_eq!(*end, [3, 4]);
/// ```
#[inline]
pub fn map_split<U: ?Sized, V: ?Sized, F>(orig: Ref<'b, T>, f: F) -> (Ref<'b, U>, Ref<'b, V>)
where F: FnOnce(&T) -> (&U, &V)
{
let (a, b) = f(orig.value);
let borrow = orig.borrow.clone();
(Ref { value: a, borrow }, Ref { value: b, borrow: orig.borrow })
}
/// Make a new `RefVal` from the borrowed data.
///
/// The `RefCell` is already immutably borrowed, so this operation
/// cannot fail.
#[inline]
pub fn map_val<U: Sized, F>(orig: Ref<'b, T>, f: F) -> RefVal<'b, U>
where F: FnOnce(&'b T) -> U
{
RefVal {
value: f(orig.value),
borrow: orig.borrow,
}
}
}
impl<T: ?Sized + fmt::Display> fmt::Display for Ref<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.value.fmt(f)
}
}
impl<'b, T: ?Sized> RefMut<'b, T> {
/// Makes a new `RefMut` for a component of the borrowed data, e.g., an enum
/// variant.
///
/// The `RefCell` is already mutably borrowed, so this cannot fail.
///
/// This is an associated function that needs to be used as
/// `RefMut::map(...)`. A method would interfere with methods of the same
/// name on the contents of a `RefCell` used through `Deref`.
///
/// # Examples
///
/// ```
/// use std::cell::{RefCell, RefMut};
///
/// let c = RefCell::new((5, 'b'));
/// {
/// let b1: RefMut<(u32, char)> = c.borrow_mut();
/// let mut b2: RefMut<u32> = RefMut::map(b1, |t| &mut t.0);
/// assert_eq!(*b2, 5);
/// *b2 = 42;
/// }
/// assert_eq!(*c.borrow(), (42, 'b'));
/// ```
#[inline]
pub fn map<U: ?Sized, F>(orig: RefMut<'b, T>, f: F) -> RefMut<'b, U>
where F: FnOnce(&mut T) -> &mut U
{
// FIXME(nll-rfc#40): fix borrow-check
let RefMut { value, borrow } = orig;
RefMut {
value: f(value),
borrow,
}
}
/// Splits a `RefMut` into multiple `RefMut`s for different components of the
/// borrowed data.
///
/// The underlying `RefCell` will remain mutably borrowed until both
/// returned `RefMut`s go out of scope.
///
/// The `RefCell` is already mutably borrowed, so this cannot fail.
///
/// This is an associated function that needs to be used as
/// `RefMut::map_split(...)`. A method would interfere with methods of the
/// same name on the contents of a `RefCell` used through `Deref`.
///
/// # Examples
///
/// ```
/// use std::cell::{RefCell, RefMut};
///
/// let cell = RefCell::new([1, 2, 3, 4]);
/// let borrow = cell.borrow_mut();
/// let (mut begin, mut end) = RefMut::map_split(borrow, |slice| slice.split_at_mut(2));
/// assert_eq!(*begin, [1, 2]);
/// assert_eq!(*end, [3, 4]);
/// begin.copy_from_slice(&[4, 3]);
/// end.copy_from_slice(&[2, 1]);
/// ```
#[inline]
pub fn map_split<U: ?Sized, V: ?Sized, F>(
orig: RefMut<'b, T>, f: F
) -> (RefMut<'b, U>, RefMut<'b, V>)
where F: FnOnce(&mut T) -> (&mut U, &mut V)
{
let (a, b) = f(orig.value);
let borrow = orig.borrow.clone();
(RefMut { value: a, borrow }, RefMut { value: b, borrow: orig.borrow })
}
/// Make a new `RefValMut` from the borrowed data.
///
/// The `RefCell` is already immutably borrowed, so this operation
/// cannot fail.
#[inline]
pub fn map_val<U: Sized, F>(orig: RefMut<'b, T>, f: F) -> RefValMut<'b, U>
where F: FnOnce(&'b mut T) -> U
{
RefValMut {
value: f(orig.value),
borrow: orig.borrow,
}
}
}
struct BorrowRefMut<'b> {
borrow: &'b Cell<BorrowFlag>,
}
impl Drop for BorrowRefMut<'_> {
#[inline]
fn drop(&mut self) {
let borrow = self.borrow.get();
debug_assert!(is_writing(borrow));
self.borrow.set(borrow + 1);
}
}
impl<'b> BorrowRefMut<'b> {
#[inline]
fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRefMut<'b>> {
// NOTE: Unlike BorrowRefMut::clone, new is called to create the initial
// mutable reference, and so there must currently be no existing
// references. Thus, while clone increments the mutable refcount, here
// we explicitly only allow going from UNUSED to UNUSED - 1.
match borrow.get() {
UNUSED => {
borrow.set(UNUSED - 1);
Some(BorrowRefMut { borrow })
},
_ => None,
}
}
// Clone a `BorrowRefMut`.
//
// This is only valid if each `BorrowRefMut` is used to track a mutable
// reference to a distinct, nonoverlapping range of the original object.
// This isn't in a Clone impl so that code doesn't call this implicitly.
#[inline]
fn clone(&self) -> BorrowRefMut<'b> {
let borrow = self.borrow.get();
debug_assert!(is_writing(borrow));
// Prevent the borrow counter from underflowing.
assert!(borrow != isize::min_value());
self.borrow.set(borrow - 1);
BorrowRefMut { borrow: self.borrow }
}
}
/// A wrapper type for a mutably borrowed value from a `RefCell<T>`.
///
/// See the [module-level documentation](index.html) for more.
pub struct RefMut<'b, T: ?Sized + 'b> {
value: &'b mut T,
borrow: BorrowRefMut<'b>,
}
impl<T: ?Sized> Deref for RefMut<'_, T> {
type Target = T;
#[inline]
fn deref(&self) -> &T {
self.value
}
}
impl<T: ?Sized> DerefMut for RefMut<'_, T> {
#[inline]
fn deref_mut(&mut self) -> &mut T {
self.value
}
}
impl<T: ?Sized + fmt::Display> fmt::Display for RefMut<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.value.fmt(f)
}
}
/// A type containing a value that contains a borrowed reference to a
/// value from a `RefCell<T>`.
///
/// See the [module-level documentation](index.html) for more.
pub struct RefVal<'b, T> {
value: T,
borrow: BorrowRef<'b>,
}
impl<'b, T> RefVal<'b, T> {
/// Copies a `RefVal`.
///
/// The `RefCell` is already immutably borrowed, so this cannot fail.
///
/// This is an associated function that needs to be used as
/// `Ref::clone(...)`. A `Clone` implementation or a method would interfere
/// with the widespread use of `r.borrow().clone()` to clone the contents of
/// a `RefCell`.
#[inline]
pub fn clone(orig: &RefVal<'b, T>) -> RefVal<'b, T>
where T: Clone
{
RefVal {
value: orig.value.clone(),
borrow: orig.borrow.clone(),
}
}
/// Make a new `RefVal` from the another `RefVal`.
///
/// The `RefCell` is already immutably borrowed, so this operation
/// cannot fail.
#[inline]
pub fn map<U: Sized, F>(orig: RefVal<'b, T>, f: F) -> RefVal<'b, U>
where F: FnOnce(T) -> U
{
RefVal {
value: f(orig.value),
borrow: orig.borrow,
}
}
}
impl<T> Deref for RefVal<'_, T> {
type Target = T;
#[inline]
fn deref(&self) -> &T {
&self.value
}
}
impl<T> DerefMut for RefVal<'_, T> {
#[inline]
fn deref_mut(&mut self) -> &mut T {
&mut self.value
}
}
impl<T: fmt::Display> fmt::Display for RefVal<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.value.fmt(f)
}
}
/// A type containing a value that contains a borrowed mutable reference
/// to a value from a `RefCell<T>`.
///
/// See the [module-level documentation](index.html) for more.
pub struct RefValMut<'b, T> {
value: T,
borrow: BorrowRefMut<'b>,
}
impl<'b, T> RefValMut<'b, T> {
/// Make a new `RefValMut` from the another `RefValMut`.
///
/// The `RefCell` is already mutably borrowed, so this operation
/// cannot fail.
#[inline]
pub fn map<U: Sized, F>(orig: RefValMut<'b, T>, f: F) -> RefValMut<'b, U>
where F: FnOnce(T) -> U
{
RefValMut {
value: f(orig.value),
borrow: orig.borrow,
}
}
}
impl<T> Deref for RefValMut<'_, T> {
type Target = T;
#[inline]
fn deref(&self) -> &T {
&self.value
}
}
impl<T> DerefMut for RefValMut<'_, T> {
#[inline]
fn deref_mut(&mut self) -> &mut T {
&mut self.value
}
}
impl<T: fmt::Display> fmt::Display for RefValMut<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.value.fmt(f)
}
}