Enum Foster

pub enum Foster<OwnedT, FosteredT> {
    Owned(OwnedT),
    Fostered(FosteredT),
}

Fostering allows for subjective equivalence between owned values and differently-typed fostered values. Equivalence can mean comparison, iteration, hashing, representation, etc.

An example use case:

You create Vec<String> values dynamically in your program, but you also want to allow for constant values, which cannot be a Vec. A reasonable constant equivalent would be &'static [&'static str], which is a very different type.

Although you could convert &'static [&'static str] to Vec<String>, it would require allocation, which is unnecessary and wasteful in situations in which you don’t actually need or care about ownership, e.g. comparisons. (Although we can allow for efficient conversion via the IntoOwned trait.)

“Fostering” means creating a single type on top of both types, and then implementing necessary traits for that type, e.g. PartialEq.

This type simply provides a unified mechanism for fostering. Furthermore, this module contains commonly useful implementations, such as FosterString and FosterStringVector, as well as macros for delegating the implemented traits to newtypes.

Note that Cow also counts as fostering, but it’s more specific in that the fostered type is always a reference of the owned type, which allows for generalized conversion to ownership when necessary via ToOwned.

Variants

Owned(OwnedT)

Owned.

Fostered(FosteredT)

Fostered.

Implementations

impl<OwnedT, FosteredT> Foster<OwnedT, FosteredT>

pub const fn new_owned(value: OwnedT) -> Self

Constructor.

pub const fn new_fostered(value: FosteredT) -> Self

Constructor.

pub const fn is_owned(&self) -> bool

True if owned.

Trait Implementations

impl<OwnedT: Clone, FosteredT: Clone> Clone for Foster<OwnedT, FosteredT>

fn clone(&self) -> Foster<OwnedT, FosteredT>

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<OwnedT: Debug, FosteredT: Debug> Debug for Foster<OwnedT, FosteredT>

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

Formats the value using the given formatter.

impl<OwnedT, FosteredT> From<OwnedT> for Foster<OwnedT, FosteredT>

fn from(value: OwnedT) -> Self

Converts to this type from the input type.