Struct gcollections::wrappers::optional::Optional

pub struct Optional<T> {
    // some fields omitted
}

Methods

impl<T> Optional<T>

fn wrap(value: Option<T>) -> Optional<T>

fn unwrap(self) -> Option<T>

Methods from Deref<Target=Option<T>>

fn is_some(&self) -> bool

Returns true if the option is a Some value

Examples

let x: Option<u32> = Some(2);
assert_eq!(x.is_some(), true);

let x: Option<u32> = None;
assert_eq!(x.is_some(), false);

fn is_none(&self) -> bool

Returns true if the option is a None value

Examples

let x: Option<u32> = Some(2);
assert_eq!(x.is_none(), false);

let x: Option<u32> = None;
assert_eq!(x.is_none(), true);

fn as_ref(&self) -> Option<&T>

Converts from Option<T> to Option<&T>

Examples

Convert an Option<String> into an Option<usize>, preserving the original. The map method takes the self argument by value, consuming the original, so this technique uses as_ref to first take an Option to a reference to the value inside the original.

let num_as_str: Option<String> = Some("10".to_string());
// First, cast `Option<String>` to `Option<&String>` with `as_ref`,
// then consume *that* with `map`, leaving `num_as_str` on the stack.
let num_as_int: Option<usize> = num_as_str.as_ref().map(|n| n.len());
println!("still can print num_as_str: {:?}", num_as_str);

fn as_mut(&mut self) -> Option<&mut T>

Converts from Option<T> to Option<&mut T>

Examples

let mut x = Some(2);
match x.as_mut() {
    Some(v) => *v = 42,
    None => {},
}
assert_eq!(x, Some(42));

fn expect(self, msg: &str) -> T

Unwraps an option, yielding the content of a Some.

Panics

Panics if the value is a None with a custom panic message provided by msg.

Examples

let x = Some("value");
assert_eq!(x.expect("the world is ending"), "value");

let x: Option<&str> = None;
x.expect("the world is ending"); // panics with `the world is ending`

fn unwrap(self) -> T

Moves the value v out of the Option<T> if it is Some(v).

Panics

Panics if the self value equals None.

Safety note

In general, because this function may panic, its use is discouraged. Instead, prefer to use pattern matching and handle the None case explicitly.

Examples

let x = Some("air");
assert_eq!(x.unwrap(), "air");

let x: Option<&str> = None;
assert_eq!(x.unwrap(), "air"); // fails

fn unwrap_or(self, def: T) -> T

Returns the contained value or a default.

Examples

assert_eq!(Some("car").unwrap_or("bike"), "car");
assert_eq!(None.unwrap_or("bike"), "bike");

fn unwrap_or_else<F>(self, f: F) -> T where F: FnOnce() -> T

Returns the contained value or computes it from a closure.

Examples

let k = 10;
assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4);
assert_eq!(None.unwrap_or_else(|| 2 * k), 20);

fn map<U, F>(self, f: F) -> Option<U> where F: FnOnce(T) -> U

Maps an Option<T> to Option<U> by applying a function to a contained value

Examples

Convert an Option<String> into an Option<usize>, consuming the original:

let maybe_some_string = Some(String::from("Hello, World!"));
// `Option::map` takes self *by value*, consuming `maybe_some_string`
let maybe_some_len = maybe_some_string.map(|s| s.len());

assert_eq!(maybe_some_len, Some(13));

fn map_or<U, F>(self, default: U, f: F) -> U where F: FnOnce(T) -> U

Applies a function to the contained value (if any), or returns a default (if not).

Examples

let x = Some("foo");
assert_eq!(x.map_or(42, |v| v.len()), 3);

let x: Option<&str> = None;
assert_eq!(x.map_or(42, |v| v.len()), 42);

fn map_or_else<U, D, F>(self, default: D, f: F) -> U where D: FnOnce() -> U, F: FnOnce(T) -> U

Applies a function to the contained value (if any), or computes a default (if not).

Examples

let k = 21;

let x = Some("foo");
assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3);

let x: Option<&str> = None;
assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42);

fn ok_or<E>(self, err: E) -> Result<T, E>

Transforms the Option<T> into a Result<T, E>, mapping Some(v) to Ok(v) and None to Err(err).

Examples

let x = Some("foo");
assert_eq!(x.ok_or(0), Ok("foo"));

let x: Option<&str> = None;
assert_eq!(x.ok_or(0), Err(0));

fn ok_or_else<E, F>(self, err: F) -> Result<T, E> where F: FnOnce() -> E

Transforms the Option<T> into a Result<T, E>, mapping Some(v) to Ok(v) and None to Err(err()).

Examples

let x = Some("foo");
assert_eq!(x.ok_or_else(|| 0), Ok("foo"));

let x: Option<&str> = None;
assert_eq!(x.ok_or_else(|| 0), Err(0));

fn iter(&self) -> Iter<T>

Returns an iterator over the possibly contained value.

Examples

let x = Some(4);
assert_eq!(x.iter().next(), Some(&4));

let x: Option<u32> = None;
assert_eq!(x.iter().next(), None);

fn iter_mut(&mut self) -> IterMut<T>

Returns a mutable iterator over the possibly contained value.

Examples

let mut x = Some(4);
match x.iter_mut().next() {
    Some(v) => *v = 42,
    None => {},
}
assert_eq!(x, Some(42));

let mut x: Option<u32> = None;
assert_eq!(x.iter_mut().next(), None);

fn and<U>(self, optb: Option<U>) -> Option<U>

Returns None if the option is None, otherwise returns optb.

Examples

let x = Some(2);
let y: Option<&str> = None;
assert_eq!(x.and(y), None);

let x: Option<u32> = None;
let y = Some("foo");
assert_eq!(x.and(y), None);

let x = Some(2);
let y = Some("foo");
assert_eq!(x.and(y), Some("foo"));

let x: Option<u32> = None;
let y: Option<&str> = None;
assert_eq!(x.and(y), None);

fn and_then<U, F>(self, f: F) -> Option<U> where F: FnOnce(T) -> Option<U>

Returns None if the option is None, otherwise calls f with the wrapped value and returns the result.

Some languages call this operation flatmap.

Examples

fn sq(x: u32) -> Option<u32> { Some(x * x) }
fn nope(_: u32) -> Option<u32> { None }

assert_eq!(Some(2).and_then(sq).and_then(sq), Some(16));
assert_eq!(Some(2).and_then(sq).and_then(nope), None);
assert_eq!(Some(2).and_then(nope).and_then(sq), None);
assert_eq!(None.and_then(sq).and_then(sq), None);

fn or(self, optb: Option<T>) -> Option<T>

Returns the option if it contains a value, otherwise returns optb.

Examples

let x = Some(2);
let y = None;
assert_eq!(x.or(y), Some(2));

let x = None;
let y = Some(100);
assert_eq!(x.or(y), Some(100));

let x = Some(2);
let y = Some(100);
assert_eq!(x.or(y), Some(2));

let x: Option<u32> = None;
let y = None;
assert_eq!(x.or(y), None);

fn or_else<F>(self, f: F) -> Option<T> where F: FnOnce() -> Option<T>

Returns the option if it contains a value, otherwise calls f and returns the result.

Examples

fn nobody() -> Option<&'static str> { None }
fn vikings() -> Option<&'static str> { Some("vikings") }

assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians"));
assert_eq!(None.or_else(vikings), Some("vikings"));
assert_eq!(None.or_else(nobody), None);

fn take(&mut self) -> Option<T>

Takes the value out of the option, leaving a None in its place.

Examples

let mut x = Some(2);
x.take();
assert_eq!(x, None);

let mut x: Option<u32> = None;
x.take();
assert_eq!(x, None);

fn cloned(self) -> Option<T>

Maps an Option<&T> to an Option<T> by cloning the contents of the option.

fn unwrap_or_default(self) -> T

Returns the contained value or a default

Consumes the self argument then, if Some, returns the contained value, otherwise if None, returns the default value for that type.

Examples

Convert a string to an integer, turning poorly-formed strings into 0 (the default value for integers). parse converts a string to any other type that implements FromStr, returning None on error.

let good_year_from_input = "1909";
let bad_year_from_input = "190blarg";
let good_year = good_year_from_input.parse().ok().unwrap_or_default();
let bad_year = bad_year_from_input.parse().ok().unwrap_or_default();

assert_eq!(1909, good_year);
assert_eq!(0, bad_year);

Trait Implementations

impl<T: Debug> Debug for Optional<T>

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<T: Ord> Ord for Optional<T>

fn cmp(&self, __arg_0: &Optional<T>) -> Ordering

This method returns an Ordering between self and other.

impl<T: PartialOrd> PartialOrd for Optional<T>

fn partial_cmp(&self, __arg_0: &Optional<T>) -> Option<Ordering>

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

fn lt(&self, __arg_0: &Optional<T>) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, __arg_0: &Optional<T>) -> bool

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

fn gt(&self, __arg_0: &Optional<T>) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, __arg_0: &Optional<T>) -> bool

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

impl<T: Eq> Eq for Optional<T>

impl<T: PartialEq> PartialEq for Optional<T>

fn eq(&self, __arg_0: &Optional<T>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, __arg_0: &Optional<T>) -> bool

This method tests for !=.

impl<T: Copy> Copy for Optional<T>

impl<T: Clone> Clone for Optional<T>

fn clone(&self) -> Optional<T>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T> Deref for Optional<T>

type Target = Option<T>

The resulting type after dereferencing

fn deref<'a>(&'a self) -> &'a Option<T>

The method called to dereference a value

impl<T> DerefMut for Optional<T>

fn deref_mut<'a>(&'a mut self) -> &'a mut Option<T>

The method called to mutably dereference a value

impl<T> Cardinality for Optional<T>

type Size = usize

fn size(&self) -> usize

impl<T> Singleton<T> for Optional<T>

fn singleton(value: T) -> Optional<T>

impl<T> Empty for Optional<T>

fn empty() -> Optional<T>

impl<T: Bounded> Bounded for Optional<T>

type Bound = T::Bound

fn lower(&self) -> T::Bound

fn upper(&self) -> T::Bound

impl<T> Intersection<Optional<T>> for Optional<T> where T: Clone + PartialEq

type Output = Optional<T>

fn intersection(&self, other: &Optional<T>) -> Self::Output

impl<T> Intersection<T> for Optional<T> where T: Clone + PartialEq

type Output = Optional<T>

fn intersection(&self, other: &T) -> Self::Output

impl<T> Difference<Optional<T>> for Optional<T> where T: Clone + PartialEq

type Output = Optional<T>

fn difference(&self, other: &Optional<T>) -> Self::Output

impl<T> Difference<T> for Optional<T> where T: Clone + PartialEq

type Output = Optional<T>

fn difference(&self, other: &T) -> Self::Output

impl<T, U> Disjoint<Optional<U>> for Optional<T> where T: Disjoint<U>

fn is_disjoint(&self, other: &Optional<U>) -> bool

impl<T, U> Disjoint<U> for Optional<T> where T: Disjoint<U>, U: GroundType

fn is_disjoint(&self, other: &U) -> bool

impl<T, U> Contains<U> for Optional<T> where T: Contains<U>

fn contains(&self, value: &U) -> bool

impl<T> Subset<Optional<T>> for Optional<T> where T: Subset

fn is_subset(&self, other: &Optional<T>) -> bool

impl<T> ProperSubset<Optional<T>> for Optional<T> where T: Subset + PartialEq

fn is_proper_subset(&self, other: &Optional<T>) -> bool

impl<T, U> Overlap<Optional<U>> for Optional<T> where T: Overlap<U>

fn overlap(&self, other: &Optional<U>) -> bool

impl<T, U> Overlap<U> for Optional<T> where T: Overlap<U>, U: GroundType

fn overlap(&self, other: &U) -> bool

impl<T, U> ShrinkLeft<U> for Optional<T> where T: PartialOrd<U> + Clone

fn shrink_left(&self, lb: U) -> Self

impl<T, U> ShrinkRight<U> for Optional<T> where T: PartialOrd<U> + Clone

fn shrink_right(&self, ub: U) -> Self

impl<T, U> StrictShrinkLeft<U> for Optional<T> where T: PartialOrd<U> + Clone

fn strict_shrink_left(&self, lb: U) -> Self

impl<T, U> StrictShrinkRight<U> for Optional<T> where T: PartialOrd<U> + Clone

fn strict_shrink_right(&self, ub: U) -> Self

impl<T, U, R> Add<Optional<U>> for Optional<T> where T: Add<U, Output=R>

type Output = Optional<R>

The resulting type after applying the + operator

fn add(self, other: Optional<U>) -> Self::Output

The method for the + operator

impl<T, U, R> Add<U> for Optional<T> where T: Add<U, Output=R>, U: GroundType

type Output = Optional<R>

The resulting type after applying the + operator

fn add(self, other: U) -> Self::Output

The method for the + operator

impl<T, U, R> Sub<Optional<U>> for Optional<T> where T: Sub<U, Output=R>

type Output = Optional<R>

The resulting type after applying the - operator

fn sub(self, other: Optional<U>) -> Self::Output

The method for the - operator

impl<T, U, R> Sub<U> for Optional<T> where T: Sub<U, Output=R>, U: GroundType

type Output = Optional<R>

The resulting type after applying the - operator

fn sub(self, other: U) -> Self::Output

The method for the - operator

impl<T, U, R> Mul<Optional<U>> for Optional<T> where T: Mul<U, Output=R>

type Output = Optional<R>

The resulting type after applying the * operator

fn mul(self, other: Optional<U>) -> Self::Output

The method for the * operator

impl<T, U, R> Mul<U> for Optional<T> where T: Mul<U, Output=R>, U: GroundType

type Output = Optional<R>

The resulting type after applying the * operator

fn mul(self, other: U) -> Self::Output

The method for the * operator