Struct maybe_dangling::ManuallyDrop

#[repr(transparent)]
pub struct ManuallyDrop<T> { /* private fields */ }

A wrapper to inhibit compiler from automatically calling T’s destructor. This wrapper is 0-cost.

See ::core::mem::ManuallyDrop for more info.

Differences with ::core::mem::ManuallyDrop

• No niches

  The current implementation uses ::core::mem::MaybeUninit to make sure the aliasing and dereferenceableity properties of the inner T are properly disabled.

  The main side-effect of this implementation is that it disables niches, thereby preventing discriminant elision.

  For instance, an Option<ManuallyDrop<bool>> will occupy two bytes rather than one.

• It does not implement Structural{Partial,}Eq.

• Note that once stdlib’s own ::core::mem::ManuallyDrop properly gets its aliasing/dereferenceableity properties removed, this crate shall be updated to just reëxport it (using a build.rs to prevent MSRV breakage).

  This means that the lack of discriminant elision cannot be relied upon either!

• Other than that, this is a #[repr(transparent)] wrapper around T, thereby having:

  • equal Layout;
  • equal calling-convention ABI¹

---

1. this is assuming MaybeUninit<T> has the same ABI as T, as it currently advertises, despite that probably being a bad idea for a “bag of bytes” T-ish wrapper, since it means that padding bytes inside of T won’t be preserved when working with a MaybeUninit<T>. So, if the stdlib were to break the current ABI promise of MaybeUninit to cater to that problem, then this crate would probably do so well, unless the maybe_dangling changes were to make it to the stdlib first. ↩

Implementations

impl<T> ManuallyDrop<T>

pub const fn new(value: T) -> ManuallyDrop<T>

Wrap a value to be manually dropped.

See ::core::mem::ManuallyDrop::new() for more info.

pub const fn into_inner(slot: ManuallyDrop<T>) -> T

Extracts the value from the ManuallyDrop container.

See ::core::mem::ManuallyDrop::into_inner() for more info.

pub unsafe fn take(slot: &mut ManuallyDrop<T>) -> T

Takes the value from the ManuallyDrop<T> container out.

See ::core::mem::ManuallyDrop::take() for more info.

pub unsafe fn drop(slot: &mut ManuallyDrop<T>)

Manually drops the contained value.

See ::core::mem::ManuallyDrop::drop() for more info.

Trait Implementations

impl<T: Clone> Clone for ManuallyDrop<T>

fn clone(&self) -> Self

See ::core::mem::ManuallyDrop::clone() for more info.

fn clone_from(&mut self, source: &Self)

See ::core::mem::ManuallyDrop::clone_from() for more info. See ::core::mem::ManuallyDrop::clone_from() for more info.

impl<T: Debug> Debug for ManuallyDrop<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

See ::core::mem::ManuallyDrop::fmt() for more info. See ::core::mem::ManuallyDrop::fmt() for more info.

impl<T: Default> Default for ManuallyDrop<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T> Deref for ManuallyDrop<T>

fn deref(&self) -> &T

See ::core::mem::ManuallyDrop::deref() for more info.

type Target = T

The resulting type after dereferencing.

impl<T> DerefMut for ManuallyDrop<T>

fn deref_mut(&mut self) -> &mut T

See ::core::mem::ManuallyDrop::deref_mut() for more info.

impl<T: Hash> Hash for ManuallyDrop<T>

fn hash<__H: Hasher>(&self, state: &mut __H)

See ::core::mem::ManuallyDrop::hash() for more info. See ::core::mem::ManuallyDrop::hash() for more info.

fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<T: Ord> Ord for ManuallyDrop<T>

fn cmp(&self, other: &Self) -> Ordering

See ::core::mem::ManuallyDrop::cmp() for more info. See ::core::mem::ManuallyDrop::cmp() for more info.

fn max(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Selfwhere Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd<Self>,

Restrict a value to a certain interval.

impl<T: PartialEq> PartialEq<ManuallyDrop<T>> for ManuallyDrop<T>

fn eq(&self, other: &Self) -> bool

See ::core::mem::ManuallyDrop::eq() for more info. See ::core::mem::ManuallyDrop::eq() for more info.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T: PartialOrd> PartialOrd<ManuallyDrop<T>> for ManuallyDrop<T>

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

See ::core::mem::ManuallyDrop::partial_cmp() for more info. See ::core::mem::ManuallyDrop::partial_cmp() for more info.

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl<T: Copy> Copy for ManuallyDrop<T>

impl<T: Eq> Eq for ManuallyDrop<T>