Struct wasmtime_environ::SparseMap
source · [−]pub struct SparseMap<K, V> where
K: EntityRef,
V: SparseMapValue<K>, { /* private fields */ }
Expand description
A sparse mapping of entity references.
A SparseMap<K, V>
map provides:
- Memory usage equivalent to
SecondaryMap<K, u32>
+Vec<V>
, so much smaller thanSecondaryMap<K, V>
for sparse mappings of largerV
types. - Constant time lookup, slightly slower than
SecondaryMap
. - A very fast, constant time
clear()
operation. - Fast insert and erase operations.
- Stable iteration that is as fast as a
Vec<V>
.
Compared to SecondaryMap
When should we use a SparseMap
instead of a secondary SecondaryMap
? First of all,
SparseMap
does not provide the functionality of a PrimaryMap
which can allocate and assign
entity references to objects as they are pushed onto the map. It is only the secondary entity
maps that can be replaced with a SparseMap
.
- A secondary entity map assigns a default mapping to all keys. It doesn’t distinguish between
an unmapped key and one that maps to the default value.
SparseMap
does not requireDefault
values, and it tracks accurately if a key has been mapped or not. - Iterating over the contents of an
SecondaryMap
is linear in the size of the key space, while iterating over aSparseMap
is linear in the number of elements in the mapping. This is an advantage precisely when the mapping is sparse. SparseMap::clear()
is constant time and super-fast.SecondaryMap::clear()
is linear in the size of the key space. (Or, rather the requiredresize()
call following theclear()
is).SparseMap
requires the values to implementSparseMapValue<K>
which means that they must contain their own key.
Implementations
sourceimpl<K, V> SparseMap<K, V> where
K: EntityRef,
V: SparseMapValue<K>,
impl<K, V> SparseMap<K, V> where
K: EntityRef,
V: SparseMapValue<K>,
sourcepub fn get(&self, key: K) -> Option<&V>
pub fn get(&self, key: K) -> Option<&V>
Returns a reference to the value corresponding to the key.
sourcepub fn get_mut(&mut self, key: K) -> Option<&mut V>
pub fn get_mut(&mut self, key: K) -> Option<&mut V>
Returns a mutable reference to the value corresponding to the key.
Note that the returned value must not be mutated in a way that would change its key. This would invalidate the sparse set data structure.
sourcepub fn contains_key(&self, key: K) -> bool
pub fn contains_key(&self, key: K) -> bool
Return true
if the map contains a value corresponding to key
.
sourcepub fn insert(&mut self, value: V) -> Option<V>
pub fn insert(&mut self, value: V) -> Option<V>
Insert a value into the map.
If the map did not have this key present, None
is returned.
If the map did have this key present, the value is updated, and the old value is returned.
It is not necessary to provide a key since the value knows its own key already.
sourcepub fn values(&self) -> Iter<'_, V>ⓘNotable traits for Iter<'a, T>impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;
pub fn values(&self) -> Iter<'_, V>ⓘNotable traits for Iter<'a, T>impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;
Get an iterator over the values in the map.
The iteration order is entirely determined by the preceding sequence of insert
and
remove
operations. In particular, if no elements were removed, this is the insertion
order.
Trait Implementations
sourceimpl<'de, K, V> Deserialize<'de> for SparseMap<K, V> where
K: EntityRef + Deserialize<'de>,
V: SparseMapValue<K> + Deserialize<'de>,
impl<'de, K, V> Deserialize<'de> for SparseMap<K, V> where
K: EntityRef + Deserialize<'de>,
V: SparseMapValue<K> + Deserialize<'de>,
sourcefn deserialize<__D>(
__deserializer: __D
) -> Result<SparseMap<K, V>, <__D as Deserializer<'de>>::Error> where
__D: Deserializer<'de>,
fn deserialize<__D>(
__deserializer: __D
) -> Result<SparseMap<K, V>, <__D as Deserializer<'de>>::Error> where
__D: Deserializer<'de>,
Deserialize this value from the given Serde deserializer. Read more
sourceimpl<'a, K, V> IntoIterator for &'a SparseMap<K, V> where
K: EntityRef,
V: SparseMapValue<K>,
impl<'a, K, V> IntoIterator for &'a SparseMap<K, V> where
K: EntityRef,
V: SparseMapValue<K>,
Iterating over the elements of a set.
sourceimpl<K, V> Serialize for SparseMap<K, V> where
K: EntityRef + Serialize,
V: SparseMapValue<K> + Serialize,
impl<K, V> Serialize for SparseMap<K, V> where
K: EntityRef + Serialize,
V: SparseMapValue<K> + Serialize,
sourcefn serialize<__S>(
&self,
__serializer: __S
) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error> where
__S: Serializer,
fn serialize<__S>(
&self,
__serializer: __S
) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error> where
__S: Serializer,
Serialize this value into the given Serde serializer. Read more
Auto Trait Implementations
impl<K, V> RefUnwindSafe for SparseMap<K, V> where
K: RefUnwindSafe,
V: RefUnwindSafe,
impl<K, V> Send for SparseMap<K, V> where
K: Send,
V: Send,
impl<K, V> Sync for SparseMap<K, V> where
K: Sync,
V: Sync,
impl<K, V> Unpin for SparseMap<K, V> where
K: Unpin,
V: Unpin,
impl<K, V> UnwindSafe for SparseMap<K, V> where
K: UnwindSafe,
V: UnwindSafe,
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more