Struct tract_nnef::internal::PhantomData 1.0.0[−][src]
#[lang = "phantom_data"]pub struct PhantomData<T>
where
T: ?Sized;
Zero-sized type used to mark things that “act like” they own a T
.
Adding a PhantomData<T>
field to your type tells the compiler that your
type acts as though it stores a value of type T
, even though it doesn’t
really. This information is used when computing certain safety properties.
For a more in-depth explanation of how to use PhantomData<T>
, please see
the Nomicon.
A ghastly note 👻👻👻
Though they both have scary names, PhantomData
and ‘phantom types’ are
related, but not identical. A phantom type parameter is simply a type
parameter which is never used. In Rust, this often causes the compiler to
complain, and the solution is to add a “dummy” use by way of PhantomData
.
Examples
Unused lifetime parameters
Perhaps the most common use case for PhantomData
is a struct that has an
unused lifetime parameter, typically as part of some unsafe code. For
example, here is a struct Slice
that has two pointers of type *const T
,
presumably pointing into an array somewhere:
struct Slice<'a, T> { start: *const T, end: *const T, }
The intention is that the underlying data is only valid for the
lifetime 'a
, so Slice
should not outlive 'a
. However, this
intent is not expressed in the code, since there are no uses of
the lifetime 'a
and hence it is not clear what data it applies
to. We can correct this by telling the compiler to act as if the
Slice
struct contained a reference &'a T
:
use std::marker::PhantomData; struct Slice<'a, T: 'a> { start: *const T, end: *const T, phantom: PhantomData<&'a T>, }
This also in turn requires the annotation T: 'a
, indicating
that any references in T
are valid over the lifetime 'a
.
When initializing a Slice
you simply provide the value
PhantomData
for the field phantom
:
fn borrow_vec<T>(vec: &Vec<T>) -> Slice<'_, T> { let ptr = vec.as_ptr(); Slice { start: ptr, end: unsafe { ptr.add(vec.len()) }, phantom: PhantomData, } }
Unused type parameters
It sometimes happens that you have unused type parameters which
indicate what type of data a struct is “tied” to, even though that
data is not actually found in the struct itself. Here is an
example where this arises with FFI. The foreign interface uses
handles of type *mut ()
to refer to Rust values of different
types. We track the Rust type using a phantom type parameter on
the struct ExternalResource
which wraps a handle.
use std::marker::PhantomData; use std::mem; struct ExternalResource<R> { resource_handle: *mut (), resource_type: PhantomData<R>, } impl<R: ResType> ExternalResource<R> { fn new() -> Self { let size_of_res = mem::size_of::<R>(); Self { resource_handle: foreign_lib::new(size_of_res), resource_type: PhantomData, } } fn do_stuff(&self, param: ParamType) { let foreign_params = convert_params(param); foreign_lib::do_stuff(self.resource_handle, foreign_params); } }
Ownership and the drop check
Adding a field of type PhantomData<T>
indicates that your
type owns data of type T
. This in turn implies that when your
type is dropped, it may drop one or more instances of the type
T
. This has bearing on the Rust compiler’s drop check
analysis.
If your struct does not in fact own the data of type T
, it is
better to use a reference type, like PhantomData<&'a T>
(ideally) or PhantomData<*const T>
(if no lifetime applies), so
as not to indicate ownership.
Trait Implementations
impl<T> Clone for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
pub fn clone(&self) -> PhantomData<T>
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pub fn clone_from(&mut self, source: &Self)
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impl<T> Copy for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
impl<T> Debug for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
impl<T> Default for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
pub fn default() -> PhantomData<T>
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impl<T> Eq for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
impl<T> Hash for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
pub fn hash<H>(&self, &mut H) where
H: Hasher,
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H: Hasher,
pub fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
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H: Hasher,
impl<T> Ord for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
pub fn cmp(&self, _other: &PhantomData<T>) -> Ordering
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#[must_use]pub fn max(self, other: Self) -> Self
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#[must_use]pub fn min(self, other: Self) -> Self
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#[must_use]pub fn clamp(self, min: Self, max: Self) -> Self
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impl<T> PartialEq<PhantomData<T>> for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
pub fn eq(&self, _other: &PhantomData<T>) -> bool
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#[must_use]pub fn ne(&self, other: &Rhs) -> bool
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impl<T> PartialOrd<PhantomData<T>> for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
pub fn partial_cmp(&self, _other: &PhantomData<T>) -> Option<Ordering>
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#[must_use]pub fn lt(&self, other: &Rhs) -> bool
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#[must_use]pub fn le(&self, other: &Rhs) -> bool
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#[must_use]pub fn gt(&self, other: &Rhs) -> bool
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#[must_use]pub fn ge(&self, other: &Rhs) -> bool
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impl<T> StructuralEq for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
impl<T> StructuralPartialEq for PhantomData<T> where
T: ?Sized,
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T: ?Sized,
Auto Trait Implementations
impl<T: ?Sized> RefUnwindSafe for PhantomData<T> where
T: RefUnwindSafe,
T: RefUnwindSafe,
impl<T: ?Sized> Send for PhantomData<T> where
T: Send,
T: Send,
impl<T: ?Sized> Sync for PhantomData<T> where
T: Sync,
T: Sync,
impl<T: ?Sized> Unpin for PhantomData<T> where
T: Unpin,
T: Unpin,
impl<T: ?Sized> UnwindSafe for PhantomData<T> where
T: UnwindSafe,
T: UnwindSafe,
Blanket Implementations
impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
pub fn borrow(&self) -> &TⓘNotable traits for &'_ mut R
impl<'_, R> Read for &'_ mut R where
R: Read + ?Sized, impl<'_, W> Write for &'_ mut W where
W: Write + ?Sized, impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;
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Notable traits for &'_ mut R
impl<'_, R> Read for &'_ mut R where
R: Read + ?Sized, impl<'_, W> Write for &'_ mut W where
W: Write + ?Sized, impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
pub fn borrow_mut(&mut self) -> &mut TⓘNotable traits for &'_ mut R
impl<'_, R> Read for &'_ mut R where
R: Read + ?Sized, impl<'_, W> Write for &'_ mut W where
W: Write + ?Sized, impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;
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Notable traits for &'_ mut R
impl<'_, R> Read for &'_ mut R where
R: Read + ?Sized, impl<'_, W> Write for &'_ mut W where
W: Write + ?Sized, impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'_, F> Future for &'_ mut F where
F: Future + Unpin + ?Sized, type Output = <F as Future>::Output;
impl<T> Conv for T
impl<T> Conv for T
impl<T> Downcast for T where
T: Any,
T: Any,
pub fn into_any(self: Box<T, Global>) -> Box<dyn Any + 'static, Global>ⓘNotable traits for Box<R, Global>
impl<R> Read for Box<R, Global> where
R: Read + ?Sized, impl<W> Write for Box<W, Global> where
W: Write + ?Sized, impl<I, A> Iterator for Box<I, A> where
A: Allocator,
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<F, A> Future for Box<F, A> where
F: Future + Unpin + ?Sized,
A: Allocator + 'static, type Output = <F as Future>::Output;
Notable traits for Box<R, Global>
impl<R> Read for Box<R, Global> where
R: Read + ?Sized, impl<W> Write for Box<W, Global> where
W: Write + ?Sized, impl<I, A> Iterator for Box<I, A> where
A: Allocator,
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<F, A> Future for Box<F, A> where
F: Future + Unpin + ?Sized,
A: Allocator + 'static, type Output = <F as Future>::Output;
pub fn into_any_rc(self: Rc<T>) -> Rc<dyn Any + 'static>
pub fn as_any(&self) -> &(dyn Any + 'static)
pub fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)
impl<T> DowncastSync for T where
T: Any + Send + Sync,
T: Any + Send + Sync,
impl<T> DynClone for T where
T: Clone,
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T: Clone,
pub fn __clone_box(&self, Private) -> *mut ()
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impl<T> FmtForward for T
pub fn fmt_binary(self) -> FmtBinary<Self> where
Self: Binary,
Self: Binary,
pub fn fmt_display(self) -> FmtDisplay<Self> where
Self: Display,
Self: Display,
pub fn fmt_lower_exp(self) -> FmtLowerExp<Self> where
Self: LowerExp,
Self: LowerExp,
pub fn fmt_lower_hex(self) -> FmtLowerHex<Self> where
Self: LowerHex,
Self: LowerHex,
pub fn fmt_octal(self) -> FmtOctal<Self> where
Self: Octal,
Self: Octal,
pub fn fmt_pointer(self) -> FmtPointer<Self> where
Self: Pointer,
Self: Pointer,
pub fn fmt_upper_exp(self) -> FmtUpperExp<Self> where
Self: UpperExp,
Self: UpperExp,
pub fn fmt_upper_hex(self) -> FmtUpperHex<Self> where
Self: UpperHex,
Self: UpperHex,
impl<T> From<T> for T
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T> Pipe for T where
T: ?Sized,
T: ?Sized,
pub fn pipe<R>(self, func: impl FnOnce(Self) -> R) -> R
pub fn pipe_ref<'a, R>(&'a self, func: impl FnOnce(&'a Self) -> R) -> R where
R: 'a,
R: 'a,
pub fn pipe_ref_mut<'a, R>(
&'a mut self,
func: impl FnOnce(&'a mut Self) -> R
) -> R where
R: 'a,
&'a mut self,
func: impl FnOnce(&'a mut Self) -> R
) -> R where
R: 'a,
pub fn pipe_borrow<'a, B, R>(&'a self, func: impl FnOnce(&'a B) -> R) -> R where
Self: Borrow<B>,
R: 'a,
B: 'a + ?Sized,
Self: Borrow<B>,
R: 'a,
B: 'a + ?Sized,
pub fn pipe_borrow_mut<'a, B, R>(
&'a mut self,
func: impl FnOnce(&'a mut B) -> R
) -> R where
Self: BorrowMut<B>,
R: 'a,
B: 'a + ?Sized,
&'a mut self,
func: impl FnOnce(&'a mut B) -> R
) -> R where
Self: BorrowMut<B>,
R: 'a,
B: 'a + ?Sized,
pub fn pipe_as_ref<'a, U, R>(&'a self, func: impl FnOnce(&'a U) -> R) -> R where
Self: AsRef<U>,
R: 'a,
U: 'a + ?Sized,
Self: AsRef<U>,
R: 'a,
U: 'a + ?Sized,
pub fn pipe_as_mut<'a, U, R>(
&'a mut self,
func: impl FnOnce(&'a mut U) -> R
) -> R where
Self: AsMut<U>,
R: 'a,
U: 'a + ?Sized,
&'a mut self,
func: impl FnOnce(&'a mut U) -> R
) -> R where
Self: AsMut<U>,
R: 'a,
U: 'a + ?Sized,
pub fn pipe_deref<'a, T, R>(&'a self, func: impl FnOnce(&'a T) -> R) -> R where
Self: Deref<Target = T>,
T: 'a + ?Sized,
R: 'a,
Self: Deref<Target = T>,
T: 'a + ?Sized,
R: 'a,
pub fn pipe_deref_mut<'a, T, R>(
&'a mut self,
func: impl FnOnce(&'a mut T) -> R
) -> R where
Self: DerefMut<Target = T> + Deref,
T: 'a + ?Sized,
R: 'a,
&'a mut self,
func: impl FnOnce(&'a mut T) -> R
) -> R where
Self: DerefMut<Target = T> + Deref,
T: 'a + ?Sized,
R: 'a,
impl<T> Pipe for T
impl<T> PipeAsRef for T
pub fn pipe_as_ref<'a, T, R>(&'a self, func: impl FnOnce(&'a T) -> R) -> R where
Self: AsRef<T>,
T: 'a,
R: 'a,
Self: AsRef<T>,
T: 'a,
R: 'a,
pub fn pipe_as_mut<'a, T, R>(
&'a mut self,
func: impl FnOnce(&'a mut T) -> R
) -> R where
Self: AsMut<T>,
T: 'a,
R: 'a,
&'a mut self,
func: impl FnOnce(&'a mut T) -> R
) -> R where
Self: AsMut<T>,
T: 'a,
R: 'a,
impl<T> PipeBorrow for T
pub fn pipe_borrow<'a, T, R>(&'a self, func: impl FnOnce(&'a T) -> R) -> R where
Self: Borrow<T>,
T: 'a,
R: 'a,
Self: Borrow<T>,
T: 'a,
R: 'a,
pub fn pipe_borrow_mut<'a, T, R>(
&'a mut self,
func: impl FnOnce(&'a mut T) -> R
) -> R where
Self: BorrowMut<T>,
T: 'a,
R: 'a,
&'a mut self,
func: impl FnOnce(&'a mut T) -> R
) -> R where
Self: BorrowMut<T>,
T: 'a,
R: 'a,
impl<T> PipeDeref for T
pub fn pipe_deref<'a, R>(
&'a self,
func: impl FnOnce(&'a Self::Target) -> R
) -> R where
Self: Deref,
R: 'a,
&'a self,
func: impl FnOnce(&'a Self::Target) -> R
) -> R where
Self: Deref,
R: 'a,
pub fn pipe_deref_mut<'a, R>(
&'a mut self,
func: impl FnOnce(&'a mut Self::Target) -> R
) -> R where
Self: DerefMut,
R: 'a,
&'a mut self,
func: impl FnOnce(&'a mut Self::Target) -> R
) -> R where
Self: DerefMut,
R: 'a,
impl<T> PipeRef for T
pub fn pipe_ref<'a, R>(&'a self, func: impl FnOnce(&'a Self) -> R) -> R where
R: 'a,
R: 'a,
pub fn pipe_mut<'a, R>(&'a mut self, func: impl FnOnce(&'a mut Self) -> R) -> R where
R: 'a,
R: 'a,
impl<T> Tap for T
pub fn tap(self, func: impl FnOnce(&Self)) -> Self
pub fn tap_mut(self, func: impl FnOnce(&mut Self)) -> Self
pub fn tap_borrow<B>(self, func: impl FnOnce(&B)) -> Self where
Self: Borrow<B>,
B: ?Sized,
Self: Borrow<B>,
B: ?Sized,
pub fn tap_borrow_mut<B>(self, func: impl FnOnce(&mut B)) -> Self where
Self: BorrowMut<B>,
B: ?Sized,
Self: BorrowMut<B>,
B: ?Sized,
pub fn tap_ref<R>(self, func: impl FnOnce(&R)) -> Self where
Self: AsRef<R>,
R: ?Sized,
Self: AsRef<R>,
R: ?Sized,
pub fn tap_ref_mut<R>(self, func: impl FnOnce(&mut R)) -> Self where
Self: AsMut<R>,
R: ?Sized,
Self: AsMut<R>,
R: ?Sized,
pub fn tap_deref<T>(self, func: impl FnOnce(&T)) -> Self where
Self: Deref<Target = T>,
T: ?Sized,
Self: Deref<Target = T>,
T: ?Sized,
pub fn tap_deref_mut<T>(self, func: impl FnOnce(&mut T)) -> Self where
Self: DerefMut<Target = T> + Deref,
T: ?Sized,
Self: DerefMut<Target = T> + Deref,
T: ?Sized,
pub fn tap_dbg(self, func: impl FnOnce(&Self)) -> Self
pub fn tap_mut_dbg(self, func: impl FnOnce(&mut Self)) -> Self
pub fn tap_borrow_dbg<B>(self, func: impl FnOnce(&B)) -> Self where
Self: Borrow<B>,
B: ?Sized,
Self: Borrow<B>,
B: ?Sized,
pub fn tap_borrow_mut_dbg<B>(self, func: impl FnOnce(&mut B)) -> Self where
Self: BorrowMut<B>,
B: ?Sized,
Self: BorrowMut<B>,
B: ?Sized,
pub fn tap_ref_dbg<R>(self, func: impl FnOnce(&R)) -> Self where
Self: AsRef<R>,
R: ?Sized,
Self: AsRef<R>,
R: ?Sized,
pub fn tap_ref_mut_dbg<R>(self, func: impl FnOnce(&mut R)) -> Self where
Self: AsMut<R>,
R: ?Sized,
Self: AsMut<R>,
R: ?Sized,
pub fn tap_deref_dbg<T>(self, func: impl FnOnce(&T)) -> Self where
Self: Deref<Target = T>,
T: ?Sized,
Self: Deref<Target = T>,
T: ?Sized,
pub fn tap_deref_mut_dbg<T>(self, func: impl FnOnce(&mut T)) -> Self where
Self: DerefMut<Target = T> + Deref,
T: ?Sized,
Self: DerefMut<Target = T> + Deref,
T: ?Sized,
impl<T> Tap for T
pub fn tap<F, R>(self, func: F) -> Self where
F: FnOnce(&Self) -> R,
F: FnOnce(&Self) -> R,
pub fn tap_dbg<F, R>(self, func: F) -> Self where
F: FnOnce(&Self) -> R,
F: FnOnce(&Self) -> R,
pub fn tap_mut<F, R>(self, func: F) -> Self where
F: FnOnce(&mut Self) -> R,
F: FnOnce(&mut Self) -> R,
pub fn tap_mut_dbg<F, R>(self, func: F) -> Self where
F: FnOnce(&mut Self) -> R,
F: FnOnce(&mut Self) -> R,
impl<T, U> TapAsRef<U> for T where
U: ?Sized,
U: ?Sized,
pub fn tap_ref<F, R>(self, func: F) -> Self where
Self: AsRef<T>,
F: FnOnce(&T) -> R,
Self: AsRef<T>,
F: FnOnce(&T) -> R,
pub fn tap_ref_dbg<F, R>(self, func: F) -> Self where
Self: AsRef<T>,
F: FnOnce(&T) -> R,
Self: AsRef<T>,
F: FnOnce(&T) -> R,
pub fn tap_ref_mut<F, R>(self, func: F) -> Self where
Self: AsMut<T>,
F: FnOnce(&mut T) -> R,
Self: AsMut<T>,
F: FnOnce(&mut T) -> R,
pub fn tap_ref_mut_dbg<F, R>(self, func: F) -> Self where
Self: AsMut<T>,
F: FnOnce(&mut T) -> R,
Self: AsMut<T>,
F: FnOnce(&mut T) -> R,
impl<T, U> TapBorrow<U> for T where
U: ?Sized,
U: ?Sized,
pub fn tap_borrow<F, R>(self, func: F) -> Self where
Self: Borrow<T>,
F: FnOnce(&T) -> R,
Self: Borrow<T>,
F: FnOnce(&T) -> R,
pub fn tap_borrow_dbg<F, R>(self, func: F) -> Self where
Self: Borrow<T>,
F: FnOnce(&T) -> R,
Self: Borrow<T>,
F: FnOnce(&T) -> R,
pub fn tap_borrow_mut<F, R>(self, func: F) -> Self where
Self: BorrowMut<T>,
F: FnOnce(&mut T) -> R,
Self: BorrowMut<T>,
F: FnOnce(&mut T) -> R,
pub fn tap_borrow_mut_dbg<F, R>(self, func: F) -> Self where
Self: BorrowMut<T>,
F: FnOnce(&mut T) -> R,
Self: BorrowMut<T>,
F: FnOnce(&mut T) -> R,
impl<T> TapDeref for T
pub fn tap_deref<F, R>(self, func: F) -> Self where
Self: Deref,
F: FnOnce(&Self::Target) -> R,
Self: Deref,
F: FnOnce(&Self::Target) -> R,
pub fn tap_deref_dbg<F, R>(self, func: F) -> Self where
Self: Deref,
F: FnOnce(&Self::Target) -> R,
Self: Deref,
F: FnOnce(&Self::Target) -> R,
pub fn tap_deref_mut<F, R>(self, func: F) -> Self where
Self: DerefMut,
F: FnOnce(&mut Self::Target) -> R,
Self: DerefMut,
F: FnOnce(&mut Self::Target) -> R,
pub fn tap_deref_mut_dbg<F, R>(self, func: F) -> Self where
Self: DerefMut,
F: FnOnce(&mut Self::Target) -> R,
Self: DerefMut,
F: FnOnce(&mut Self::Target) -> R,
impl<T> ToOwned for T where
T: Clone,
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T: Clone,
type Owned = T
The resulting type after obtaining ownership.
pub fn to_owned(&self) -> T
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pub fn clone_into(&self, target: &mut T)
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impl<T> TryConv for T
impl<T> TryConv for T
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,