[−][src]Struct serenity::prelude::RwLock
A reader-writer lock
This type of lock allows a number of readers or at most one writer at any point in time. The write portion of this lock typically allows modification of the underlying data (exclusive access) and the read portion of this lock typically allows for read-only access (shared access).
This lock uses a task-fair locking policy which avoids both reader and writer starvation. This means that readers trying to acquire the lock will block even if the lock is unlocked when there are writers waiting to acquire the lock. Because of this, attempts to recursively acquire a read lock within a single thread may result in a deadlock.
The type parameter T
represents the data that this lock protects. It is
required that T
satisfies Send
to be shared across threads and Sync
to
allow concurrent access through readers. The RAII guards returned from the
locking methods implement Deref
(and DerefMut
for the write
methods)
to allow access to the contained of the lock.
Fairness
A typical unfair lock can often end up in a situation where a single thread quickly acquires and releases the same lock in succession, which can starve other threads waiting to acquire the rwlock. While this improves performance because it doesn't force a context switch when a thread tries to re-acquire a rwlock it has just released, this can starve other threads.
This rwlock uses eventual fairness to ensure that the lock will be fair on average without sacrificing performance. This is done by forcing a fair unlock on average every 0.5ms, which will force the lock to go to the next thread waiting for the rwlock.
Additionally, any critical section longer than 1ms will always use a fair unlock, which has a negligible performance impact compared to the length of the critical section.
You can also force a fair unlock by calling RwLockReadGuard::unlock_fair
or RwLockWriteGuard::unlock_fair
when unlocking a mutex instead of simply
dropping the guard.
Differences from the standard library RwLock
- Supports atomically downgrading a write lock into a read lock.
- Task-fair locking policy instead of an unspecified platform default.
- No poisoning, the lock is released normally on panic.
- Only requires 1 word of space, whereas the standard library boxes the
RwLock
due to platform limitations. - Can be statically constructed (requires the
const_fn
nightly feature). - Does not require any drop glue when dropped.
- Inline fast path for the uncontended case.
- Efficient handling of micro-contention using adaptive spinning.
- Allows raw locking & unlocking without a guard.
- Supports eventual fairness so that the rwlock is fair on average.
- Optionally allows making the rwlock fair by calling
RwLockReadGuard::unlock_fair
andRwLockWriteGuard::unlock_fair
.
Examples
use parking_lot::RwLock; let lock = RwLock::new(5); // many reader locks can be held at once { let r1 = lock.read(); let r2 = lock.read(); assert_eq!(*r1, 5); assert_eq!(*r2, 5); } // read locks are dropped at this point // only one write lock may be held, however { let mut w = lock.write(); *w += 1; assert_eq!(*w, 6); } // write lock is dropped here
Methods
impl<T> RwLock<T>
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impl<T> RwLock<T>
pub fn new(val: T) -> RwLock<T>
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pub fn new(val: T) -> RwLock<T>
Creates a new instance of an RwLock<T>
which is unlocked.
Examples
use parking_lot::RwLock; let lock = RwLock::new(5);
pub fn into_inner(self) -> T
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pub fn into_inner(self) -> T
Consumes this RwLock
, returning the underlying data.
impl<T> RwLock<T> where
T: ?Sized,
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impl<T> RwLock<T> where
T: ?Sized,
pub fn read(&self) -> RwLockReadGuard<T>
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pub fn read(&self) -> RwLockReadGuard<T>
Locks this rwlock with shared read access, blocking the current thread until it can be acquired.
The calling thread will be blocked until there are no more writers which hold the lock. There may be other readers currently inside the lock when this method returns.
Note that attempts to recursively acquire a read lock on a RwLock
when
the current thread already holds one may result in a deadlock.
Returns an RAII guard which will release this thread's shared access once it is dropped.
pub fn try_read(&self) -> Option<RwLockReadGuard<T>>
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pub fn try_read(&self) -> Option<RwLockReadGuard<T>>
Attempts to acquire this rwlock with shared read access.
If the access could not be granted at this time, then None
is returned.
Otherwise, an RAII guard is returned which will release the shared access
when it is dropped.
This function does not block.
pub fn try_read_for(&self, timeout: Duration) -> Option<RwLockReadGuard<T>>
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pub fn try_read_for(&self, timeout: Duration) -> Option<RwLockReadGuard<T>>
Attempts to acquire this rwlock with shared read access until a timeout is reached.
If the access could not be granted before the timeout expires, then
None
is returned. Otherwise, an RAII guard is returned which will
release the shared access when it is dropped.
pub fn try_read_until(&self, timeout: Instant) -> Option<RwLockReadGuard<T>>
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pub fn try_read_until(&self, timeout: Instant) -> Option<RwLockReadGuard<T>>
Attempts to acquire this rwlock with shared read access until a timeout is reached.
If the access could not be granted before the timeout expires, then
None
is returned. Otherwise, an RAII guard is returned which will
release the shared access when it is dropped.
pub fn read_recursive(&self) -> RwLockReadGuard<T>
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pub fn read_recursive(&self) -> RwLockReadGuard<T>
Locks this rwlock with shared read access, blocking the current thread until it can be acquired.
The calling thread will be blocked until there are no more writers which hold the lock. There may be other readers currently inside the lock when this method returns.
Unlike read
, this method is guaranteed to succeed without blocking if
another read lock is held at the time of the call. This allows a thread
to recursively lock a RwLock
. However using this method can cause
writers to starve since readers no longer block if a writer is waiting
for the lock.
Returns an RAII guard which will release this thread's shared access once it is dropped.
pub fn try_read_recursive(&self) -> Option<RwLockReadGuard<T>>
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pub fn try_read_recursive(&self) -> Option<RwLockReadGuard<T>>
Attempts to acquire this rwlock with shared read access.
If the access could not be granted at this time, then None
is returned.
Otherwise, an RAII guard is returned which will release the shared access
when it is dropped.
This method is guaranteed to succeed if another read lock is held at the
time of the call. See the documentation for read_recursive
for details.
This function does not block.
pub fn try_read_recursive_for(
&self,
timeout: Duration
) -> Option<RwLockReadGuard<T>>
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pub fn try_read_recursive_for(
&self,
timeout: Duration
) -> Option<RwLockReadGuard<T>>
Attempts to acquire this rwlock with shared read access until a timeout is reached.
If the access could not be granted before the timeout expires, then
None
is returned. Otherwise, an RAII guard is returned which will
release the shared access when it is dropped.
This method is guaranteed to succeed without blocking if another read
lock is held at the time of the call. See the documentation for
read_recursive
for details.
pub fn try_read_recursive_until(
&self,
timeout: Instant
) -> Option<RwLockReadGuard<T>>
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pub fn try_read_recursive_until(
&self,
timeout: Instant
) -> Option<RwLockReadGuard<T>>
Attempts to acquire this rwlock with shared read access until a timeout is reached.
If the access could not be granted before the timeout expires, then
None
is returned. Otherwise, an RAII guard is returned which will
release the shared access when it is dropped.
pub fn write(&self) -> RwLockWriteGuard<T>
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pub fn write(&self) -> RwLockWriteGuard<T>
Locks this rwlock with exclusive write access, blocking the current thread until it can be acquired.
This function will not return while other writers or other readers currently have access to the lock.
Returns an RAII guard which will drop the write access of this rwlock when dropped.
pub fn try_write(&self) -> Option<RwLockWriteGuard<T>>
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pub fn try_write(&self) -> Option<RwLockWriteGuard<T>>
Attempts to lock this rwlock with exclusive write access.
If the lock could not be acquired at this time, then None
is returned.
Otherwise, an RAII guard is returned which will release the lock when
it is dropped.
This function does not block.
pub fn try_write_for(&self, timeout: Duration) -> Option<RwLockWriteGuard<T>>
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pub fn try_write_for(&self, timeout: Duration) -> Option<RwLockWriteGuard<T>>
Attempts to acquire this rwlock with exclusive write access until a timeout is reached.
If the access could not be granted before the timeout expires, then
None
is returned. Otherwise, an RAII guard is returned which will
release the exclusive access when it is dropped.
pub fn try_write_until(&self, timeout: Instant) -> Option<RwLockWriteGuard<T>>
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pub fn try_write_until(&self, timeout: Instant) -> Option<RwLockWriteGuard<T>>
Attempts to acquire this rwlock with exclusive write access until a timeout is reached.
If the access could not be granted before the timeout expires, then
None
is returned. Otherwise, an RAII guard is returned which will
release the exclusive access when it is dropped.
pub fn upgradable_read(&self) -> RwLockUpgradableReadGuard<T>
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pub fn upgradable_read(&self) -> RwLockUpgradableReadGuard<T>
Locks this rwlock with upgradable read access, blocking the current thread until it can be acquired.
The calling thread will be blocked until there are no more writers or other upgradable reads which hold the lock. There may be other readers currently inside the lock when this method returns.
Returns an RAII guard which will release this thread's shared access once it is dropped.
pub fn try_upgradable_read(&self) -> Option<RwLockUpgradableReadGuard<T>>
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pub fn try_upgradable_read(&self) -> Option<RwLockUpgradableReadGuard<T>>
Attempts to acquire this rwlock with upgradable read access.
If the access could not be granted at this time, then None
is returned.
Otherwise, an RAII guard is returned which will release the shared access
when it is dropped.
This function does not block.
pub fn try_upgradable_read_for(
&self,
timeout: Duration
) -> Option<RwLockUpgradableReadGuard<T>>
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pub fn try_upgradable_read_for(
&self,
timeout: Duration
) -> Option<RwLockUpgradableReadGuard<T>>
Attempts to acquire this rwlock with upgradable read access until a timeout is reached.
If the access could not be granted before the timeout expires, then
None
is returned. Otherwise, an RAII guard is returned which will
release the shared access when it is dropped.
pub fn try_upgradable_read_until(
&self,
timeout: Instant
) -> Option<RwLockUpgradableReadGuard<T>>
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pub fn try_upgradable_read_until(
&self,
timeout: Instant
) -> Option<RwLockUpgradableReadGuard<T>>
Attempts to acquire this rwlock with upgradable read access until a timeout is reached.
If the access could not be granted before the timeout expires, then
None
is returned. Otherwise, an RAII guard is returned which will
release the shared access when it is dropped.
pub fn get_mut(&mut self) -> &mut T
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pub fn get_mut(&mut self) -> &mut T
Returns a mutable reference to the underlying data.
Since this call borrows the RwLock
mutably, no actual locking needs to
take place---the mutable borrow statically guarantees no locks exist.
pub unsafe fn raw_unlock_read(&self)
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pub unsafe fn raw_unlock_read(&self)
Releases shared read access of the rwlock.
Safety
This function must only be called if the rwlock was locked using
raw_read
or raw_try_read
, or if an RwLockReadGuard
from this
rwlock was leaked (e.g. with mem::forget
). The rwlock must be locked
with shared read access.
pub unsafe fn raw_unlock_write(&self)
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pub unsafe fn raw_unlock_write(&self)
Releases exclusive write access of the rwlock.
Safety
This function must only be called if the rwlock was locked using
raw_write
or raw_try_write
, or if an RwLockWriteGuard
from this
rwlock was leaked (e.g. with mem::forget
). The rwlock must be locked
with exclusive write access.
pub unsafe fn raw_unlock_upgradable_read(&self)
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pub unsafe fn raw_unlock_upgradable_read(&self)
Releases upgradable read access of the rwlock.
Safety
This function must only be called if the rwlock was locked using
raw_upgradable_read
or raw_try_upgradable_read
, or if an
RwLockUpgradableReadGuard
from this rwlock was leaked (e.g. with
mem::forget
). The rwlock must be locked with upgradable read access.
pub unsafe fn raw_unlock_read_fair(&self)
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pub unsafe fn raw_unlock_read_fair(&self)
Releases shared read access of the rwlock using a fair unlock protocol.
See RwLockReadGuard::unlock_fair
.
Safety
This function must only be called if the rwlock was locked using
raw_write
or raw_try_write
, a raw upgradable read lock was upgraded
using raw_upgrade
or raw_try_upgrade
, or if an RwLockWriteGuard
from this rwlock was leaked (e.g. with mem::forget
). The rwlock must
be locked with exclusive write access.
pub unsafe fn raw_unlock_write_fair(&self)
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pub unsafe fn raw_unlock_write_fair(&self)
Releases exclusive write access of the rwlock using a fair unlock protocol.
See RwLockWriteGuard::unlock_fair
.
Safety
This function must only be called if the rwlock was locked using
raw_write
or raw_try_write
, a raw upgradable read lock was upgraded
using raw_upgrade
or raw_try_upgrade
, or if an RwLockWriteGuard
from this rwlock was leaked (e.g. with mem::forget
). The rwlock must
be locked with exclusive write access.
pub unsafe fn raw_unlock_upgradable_read_fair(&self)
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pub unsafe fn raw_unlock_upgradable_read_fair(&self)
Releases upgradable read access of the rwlock using a fair unlock protocol.
Safety
This function must only be called if the rwlock was locked using
raw_upgradable_read
or raw_try_upgradable_read
, or if an
RwLockUpgradableReadGuard
from this rwlock was leaked (e.g. with
mem::forget
). The rwlock must be locked with upgradable read access.
pub unsafe fn raw_downgrade(&self)
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pub unsafe fn raw_downgrade(&self)
Atomically downgrades a write lock into a shared read lock without allowing any writers to take exclusive access of the lock in the meantime.
See RwLockWriteGuard::downgrade
.
Safety
This function must only be called if the rwlock was locked using
raw_write
or raw_try_write
, or if an RwLockWriteGuard
from this
rwlock was leaked (e.g. with mem::forget
). The rwlock must be locked
with exclusive write access.
pub unsafe fn raw_downgrade_upgradable_read(&self)
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pub unsafe fn raw_downgrade_upgradable_read(&self)
Atomically downgrades an upgradable read lock into a shared read lock without allowing any writers to take exclusive access of the lock in the meantime.
See RwLockUpgradableReadGuard::downgrade
.
Safety
This function must only be called if the rwlock was locked using
raw_upgradable_read
or raw_try_upgradable_read
, or if an
RwLockUpgradableReadGuard
from this rwlock was leaked (e.g. with
mem::forget
). The rwlock must be locked with upgradable read access.
impl RwLock<()>
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impl RwLock<()>
pub fn raw_read(&self)
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pub fn raw_read(&self)
Locks this rwlock with shared read access, blocking the current thread until it can be acquired.
This is similar to read
, except that a RwLockReadGuard
is not
returned. Instead you will need to call raw_unlock
to release the
rwlock.
pub fn raw_try_read(&self) -> bool
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pub fn raw_try_read(&self) -> bool
Attempts to acquire this rwlock with shared read access.
This is similar to try_read
, except that a RwLockReadGuard
is not
returned. Instead you will need to call raw_unlock
to release the
rwlock.
pub fn raw_read_recursive(&self)
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pub fn raw_read_recursive(&self)
Locks this rwlock with shared read access, blocking the current thread until it can be acquired.
This is similar to read_recursive
, except that a RwLockReadGuard
is
not returned. Instead you will need to call raw_unlock
to release the
rwlock.
pub fn raw_try_read_recursive(&self) -> bool
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pub fn raw_try_read_recursive(&self) -> bool
Attempts to acquire this rwlock with shared read access.
This is similar to try_read_recursive
, except that a RwLockReadGuard
is not
returned. Instead you will need to call raw_unlock
to release the
rwlock.
pub fn raw_write(&self)
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pub fn raw_write(&self)
Locks this rwlock with exclusive write access, blocking the current thread until it can be acquired.
This is similar to write
, except that a RwLockReadGuard
is not
returned. Instead you will need to call raw_unlock
to release the
rwlock.
pub fn raw_try_write(&self) -> bool
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pub fn raw_try_write(&self) -> bool
Attempts to lock this rwlock with exclusive write access.
This is similar to try_write
, except that a RwLockReadGuard
is not
returned. Instead you will need to call raw_unlock
to release the
rwlock.
pub fn raw_upgradable_read(&self)
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pub fn raw_upgradable_read(&self)
Locks this rwlock with upgradable read access, blocking the current thread until it can be acquired.
This is similar to upgradable_read
, except that a
RwLockUpgradableReadGuard
is not returned. Instead you will need to call
raw_unlock
to release the rwlock.
pub fn raw_try_upgradable_read(&self) -> bool
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pub fn raw_try_upgradable_read(&self) -> bool
Attempts to acquire this rwlock with upgradable read access.
This is similar to try_upgradable_read
, except that a
RwLockUpgradableReadGuard
is not returned. Instead you will need to call
raw_unlock
to release the rwlock.
pub unsafe fn raw_upgrade(&self)
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pub unsafe fn raw_upgrade(&self)
Upgrades this rwlock from upgradable read access to exclusive write access, blocking the current thread until it can be acquired.
See RwLockUpgradableReadGuard::upgrade
.
Safety
This function must only be called if the rwlock was locked using
raw_upgradable_read
or raw_try_upgradable_read
, or if an
RwLockUpgradableReadGuard
from this rwlock was leaked (e.g. with
mem::forget
). The rwlock must be locked with upgradable read access.
pub unsafe fn raw_try_upgrade(&self) -> bool
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pub unsafe fn raw_try_upgrade(&self) -> bool
Attempts to upgrade this rwlock from upgradable read access to exclusive write access.
See RwLockUpgradableReadGuard::try_upgrade
.
Safety
This function must only be called if the rwlock was locked using
raw_upgradable_read
or raw_try_upgradable_read
, or if an
RwLockUpgradableReadGuard
from this rwlock was leaked (e.g. with
mem::forget
). The rwlock must be locked with upgradable read access.
Trait Implementations
impl<T> Send for RwLock<T> where
T: Send + ?Sized,
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impl<T> Send for RwLock<T> where
T: Send + ?Sized,
impl<T> Default for RwLock<T> where
T: Default + ?Sized,
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impl<T> Default for RwLock<T> where
T: Default + ?Sized,
impl<T> Sync for RwLock<T> where
T: Send + Sync + ?Sized,
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impl<T> Sync for RwLock<T> where
T: Send + Sync + ?Sized,
impl<T> Debug for RwLock<T> where
T: Debug + ?Sized,
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impl<T> Debug for RwLock<T> where
T: Debug + ?Sized,
Blanket Implementations
impl<T, U> Into for T where
U: From<T>,
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impl<T, U> Into for T where
U: From<T>,
impl<T> From for T
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impl<T> From for T
impl<T, U> TryFrom for T where
T: From<U>,
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impl<T, U> TryFrom for T where
T: From<U>,
type Error = !
try_from
)The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
try_from
)Performs the conversion.
impl<T> Borrow for T where
T: ?Sized,
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impl<T> Borrow for T where
T: ?Sized,
impl<T> BorrowMut for T where
T: ?Sized,
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impl<T> BorrowMut for T where
T: ?Sized,
fn borrow_mut(&mut self) -> &mut T
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fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
impl<T, U> TryInto for T where
U: TryFrom<T>,
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impl<T, U> TryInto for T where
U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
try_from
)The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>
try_from
)Performs the conversion.
impl<T> Any for T where
T: 'static + ?Sized,
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impl<T> Any for T where
T: 'static + ?Sized,
fn get_type_id(&self) -> TypeId
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fn get_type_id(&self) -> TypeId
🔬 This is a nightly-only experimental API. (get_type_id
)
this method will likely be replaced by an associated static
Gets the TypeId
of self
. Read more
impl<T> Erased for T
impl<T> Erased for T
impl<T> Typeable for T where
T: Any,
impl<T> Typeable for T where
T: Any,
impl<T> DebugAny for T where
T: Any + Debug,
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impl<T> DebugAny for T where
T: Any + Debug,
impl<T> UnsafeAny for T where
T: Any,
impl<T> UnsafeAny for T where
T: Any,