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Add more methods in Cell for non-Copy types #39715

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Add more methods in Cell for non-Copy types #39715

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19c0c7b
Add more methods in Cell for non-Copy types
Feb 10, 2017
3775c4d
ensure panic safety
F001 Feb 10, 2017
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109 changes: 107 additions & 2 deletions src/libcore/cell.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -186,6 +186,7 @@ use fmt::{self, Debug, Display};
use marker::Unsize;
use mem;
use ops::{Deref, DerefMut, CoerceUnsized};
use ptr;

/// A mutable memory location.
///
Expand Down Expand Up @@ -280,6 +281,19 @@ unsafe impl<T> Send for Cell<T> where T: Send {}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> !Sync for Cell<T> {}

#[unstable(feature = "move_cell", issue = "39264")]
impl<T:Clone> Clone for Cell<T> {
#[inline]
default fn clone(&self) -> Cell<T> {
// convert `*mut T` to `&T`, because we can ensure that
// there are no mutations or mutable aliases going on when casting to &T.
let inner : &T = unsafe { self.value.get().as_ref().unwrap() };
// If `clone` panics, the `Cell` itself is in a valid state.
let another = inner.clone();
Cell::new(another)
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T:Copy> Clone for Cell<T> {
#[inline]
Expand All @@ -289,14 +303,26 @@ impl<T:Copy> Clone for Cell<T> {
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T:Default + Copy> Default for Cell<T> {
impl<T:Default> Default for Cell<T> {
/// Creates a `Cell<T>`, with the `Default` value for T.
#[inline]
fn default() -> Cell<T> {
Cell::new(Default::default())
}
}

#[unstable(feature = "move_cell", issue = "39264")]
impl<T:PartialEq> PartialEq for Cell<T> {
#[inline]
default fn eq(&self, other: &Cell<T>) -> bool {
if ptr::eq(self, other) {
true
} else {
unsafe { Cell::take_and_restore(self, other, |l, r| l == r) }
}
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T:PartialEq + Copy> PartialEq for Cell<T> {
#[inline]
Expand All @@ -305,9 +331,60 @@ impl<T:PartialEq + Copy> PartialEq for Cell<T> {
}
}

#[unstable(feature = "move_cell", issue = "39264")]
impl<T:Eq> Eq for Cell<T> {}

#[stable(feature = "cell_eq", since = "1.2.0")]
impl<T:Eq + Copy> Eq for Cell<T> {}

#[unstable(feature = "move_cell", issue = "39264")]
impl<T:PartialOrd> PartialOrd for Cell<T> {
#[inline]
default fn partial_cmp(&self, other: &Cell<T>) -> Option<Ordering> {
if ptr::eq(self, other) {
Some(Ordering::Equal)
} else {
unsafe { Cell::take_and_restore(self, other, |l, r| l.partial_cmp(r)) }
}
}

#[inline]
default fn lt(&self, other: &Cell<T>) -> bool {
if ptr::eq(self, other) {
true
} else {
unsafe { Cell::take_and_restore(self, other, |l, r| l < r) }
}
}

#[inline]
default fn le(&self, other: &Cell<T>) -> bool {
if ptr::eq(self, other) {
true
} else {
unsafe { Cell::take_and_restore(self, other, |l, r| l <= r) }
}
}

#[inline]
default fn gt(&self, other: &Cell<T>) -> bool {
if ptr::eq(self, other) {
true
} else {
unsafe { Cell::take_and_restore(self, other, |l, r| l > r) }
}
}

#[inline]
default fn ge(&self, other: &Cell<T>) -> bool {
if ptr::eq(self, other) {
true
} else {
unsafe { Cell::take_and_restore(self, other, |l, r| l >= r) }
}
}
}

#[stable(feature = "cell_ord", since = "1.10.0")]
impl<T:PartialOrd + Copy> PartialOrd for Cell<T> {
#[inline]
Expand Down Expand Up @@ -336,6 +413,18 @@ impl<T:PartialOrd + Copy> PartialOrd for Cell<T> {
}
}

#[unstable(feature = "move_cell", issue = "39264")]
impl<T:Ord> Ord for Cell<T> {
#[inline]
default fn cmp(&self, other: &Cell<T>) -> Ordering {
if ptr::eq(self, other) {
Ordering::Equal
} else {
unsafe { Cell::take_and_restore(self, other, |l, r| l.cmp(r)) }
}
}
}

#[stable(feature = "cell_ord", since = "1.10.0")]
impl<T:Ord + Copy> Ord for Cell<T> {
#[inline]
Expand All @@ -345,7 +434,7 @@ impl<T:Ord + Copy> Ord for Cell<T> {
}

#[stable(feature = "cell_from", since = "1.12.0")]
impl<T: Copy> From<T> for Cell<T> {
impl<T> From<T> for Cell<T> {
fn from(t: T) -> Cell<T> {
Cell::new(t)
}
Expand Down Expand Up @@ -422,6 +511,22 @@ impl<T> Cell<T> {
pub fn into_inner(self) -> T {
unsafe { self.value.into_inner() }
}

/// Private function used for implementing other methods when `T` is not `Copy`.
///
/// This is `unsafe` because `left` and `right` may point to the same object.
#[unstable(feature = "move_cell", issue = "39264")]
unsafe fn take_and_restore<Result, F>(left: &Self, right: &Self, f: F) -> Result
where F: FnOnce(&T, &T) -> Result
{
// convert `*mut T` to `&T`, because we can ensure that
// there are no mutations or mutable aliases going on when casting to &T.
let lhs = left.value.get().as_ref().unwrap();
let rhs = right.value.get().as_ref().unwrap();
// If panic happens in `f`, both `Cell`s are in a valid state.
let result = f(lhs, rhs);
return result;
}
}

impl<T: Default> Cell<T> {
Expand Down