Enum Attested 

pub enum Attested<T> {
    Known(T),
    AbsentFromWork,
    Unknown,
}

What is known about one field of a Reference.

See the module documentation for why the absent and unknown cases are separate variants rather than one Option.

Deliberately not #[non_exhaustive]. The three states are the model, and the defect this type exists to prevent is precisely a caller folding two of them into one arm. Closing the set makes every consumer’s match a compile error the day a fourth epistemic state is proposed — which is when that proposal should be argued, rather than absorbed by a wildcard.

Variants

Known(T)

We hold the value.

AbsentFromWork

Somebody looked, and the work has none. A renderer may act on this: a work with no date is cited n.d., a work with no publisher simply omits that element.

Unknown

Nobody has looked this up. It is not a fact about the work at all — only a record of our own ignorance — and no renderer may turn it into output.

Implementations

impl<T> Attested<T>

pub fn known(&self) -> Option<&T>

The value, if we hold one.

pub fn is_known(&self) -> bool

Whether we hold a value.

pub fn is_absent_from_work(&self) -> bool

Whether somebody established that the work has no such value.

pub fn is_unknown(&self) -> bool

Whether nobody has looked this up.

Trait Implementations

impl<T: Clone> Clone for Attested<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for Attested<T>

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

Formats the value using the given formatter.

impl<T> Default for Attested<T>

Attested::Unknown, always.

Implemented by hand rather than derived: #[derive(Default)] would demand T: Default for no reason, and — more to the point — the default has to be the state that refuses, so that a record assembled field by field cannot acquire a citable-looking hole.

fn default() -> Self

Returns the “default value” for a type.

impl<'de, T> Deserialize<'de> for Attested<T>

where T: Deserialize<'de>,

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<T: Eq> Eq for Attested<T>

impl<T: Ord> Ord for Attested<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.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

🔬This is a nightly-only experimental API. (clamp_to)

Restrict a value to a certain range.

impl<T: PartialEq> PartialEq for Attested<T>

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

Equality operator ==.

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

Inequality operator !=.

impl<T: PartialOrd> PartialOrd for Attested<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<T> Serialize for Attested<T>

where T: Serialize,

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl<T: PartialEq> StructuralPartialEq for Attested<T>