Enum CowArc

pub enum CowArc<'a, T: ?Sized + 'static> {
    Borrowed(&'a T),
    Static(&'static T),
    Owned(Arc<T>),
}

Much like a Cow, but owned values are Arc-ed to make clones cheap. This should be used for values that are cloned for use across threads and change rarely (if ever).

This also makes an opinionated tradeoff by adding a CowArc::Static and implementing From<&'static T> instead of From<'a T>. This preserves the static context and prevents conversion to CowArc::Owned in cases where a reference is known to be static. This is an optimization that prevents allocations and atomic ref-counting.

This means that static references should prefer CowArc::from or CowArc::Static and non-static references must use CowArc::Borrowed.

Variants

Borrowed(&'a T)

A borrowed value.

Static(&'static T)

A static value reference.

This exists to avoid conversion to CowArc::Owned in cases where a reference is known to be static. This is an optimization that prevents allocations and atomic ref-counting.

Owned(Arc<T>)

An owned Arc-ed value.

Implementations

impl<T: ?Sized + 'static> CowArc<'static, T>

pub fn new_owned(value: T) -> Self

where T: Sized,

Creates a new CowArc::Owned from a value.

This is simply a convenience method; the value will be wrapped in an Arc.

Note that T must be Sized: use the enum constructor directly if T is unsized.

pub fn new_owned_from_arc(value: impl Into<Arc<T>>) -> Self

Creates a new CowArc::Owned from an Arc-like value.

The Arc will be moved into the CowArc.

impl<T: ?Sized> CowArc<'static, T>

pub fn as_static(self) -> Self

Indicates this CowArc should have a static lifetime.

This ensures if this was created with a value Borrowed(&'static T), it is replaced with Static(&'static T). It is only possible to call this method if 'a is 'static. This has no effect if this is Owned(Arc<T>).

impl<'a, T: ?Sized> CowArc<'a, T>

where &'a T: Into<Arc<T>>,

pub fn into_owned(self) -> CowArc<'static, T>

Converts this into an “owned” value.

If internally a value is borrowed, it will be cloned into an “owned Arc”. If it is already a CowArc::Owned or a CowArc::Static, it will remain unchanged.

pub fn clone_owned(&self) -> CowArc<'static, T>

Clones into an owned [CowArc<'static>].

If internally a value is borrowed, it will be cloned into an “owned Arc”. If it is already a CowArc::Owned or CowArc::Static, the value will be cloned. This is equivalent to .clone().into_owned().

Trait Implementations

impl<'a, T: ?Sized> AsRef<T> for CowArc<'a, T>

fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.

impl<'a, T: ?Sized> Borrow<T> for CowArc<'a, T>

fn borrow(&self) -> &T

Immutably borrows from an owned value.

impl<'a, T: ?Sized> Clone for CowArc<'a, T>

fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'a, T: Debug + ?Sized> Debug for CowArc<'a, T>

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

Formats the value using the given formatter.

impl Default for CowArc<'static, Path>

fn default() -> Self

Returns an empty Path, wrapped in CowArc::Static.

This is equivalent to CowArc::Static(Path::new("")).

impl Default for CowArc<'static, str>

fn default() -> Self

Returns the “default value” for a type.

impl<'a, T: ?Sized> Deref for CowArc<'a, T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<'a, T: Display + ?Sized> Display for CowArc<'a, T>

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

Formats the value using the given formatter.

impl<'a> From<&'a String> for CowArc<'a, str>

fn from(value: &'a String) -> Self

Converts to this type from the input type.

impl<T: ?Sized> From<&'static T> for CowArc<'static, T>

fn from(value: &'static T) -> Self

Converts to this type from the input type.

impl From<&'static str> for CowArc<'static, Path>

fn from(value: &'static str) -> Self

Converts to this type from the input type.

impl<T> From<Arc<T>> for CowArc<'static, T>

fn from(value: Arc<T>) -> Self

Converts to this type from the input type.

impl From<PathBuf> for CowArc<'static, Path>

fn from(value: PathBuf) -> Self

Converts to this type from the input type.

impl From<String> for CowArc<'static, str>

fn from(value: String) -> Self

Converts to this type from the input type.

impl<'a, T: Hash + ?Sized> Hash for CowArc<'a, T>

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

Feeds this value into the given Hasher.

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<'a, T: Ord + ?Sized> Ord for CowArc<'a, T>

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

This method returns an Ordering between self and other.

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

where Self: Sized,

Compares and returns the maximum of two values.

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

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl<'a, T: PartialEq + ?Sized> PartialEq for CowArc<'a, T>

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

Tests for self and other values to be equal, and is used by ==.

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

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

impl<'a, T: PartialOrd + ?Sized> PartialOrd for CowArc<'a, T>

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

This method returns an ordering between self and other values if one exists.

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

Tests less than (for self and other) and is used by the < operator.

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

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

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

Tests greater than (for self and other) and is used by the > operator.

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

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

impl<'a, T: PartialEq + ?Sized> Eq for CowArc<'a, T>