Enum tokio_jsonrpc::macro_exports::Option1.0.0 [−] [src]

pub enum Option<T> {
    None,
    Some(T),
}

The Option type. See the module level documentation for more.

Variants

No value

Some value T

Methods

impl<T> Option<T>
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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);

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);

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);

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));

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`

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

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

Panics

Panics if the self value equals None.

Examples

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

Returns the contained value or a default.

Examples

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

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);

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));

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);

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);

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));

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));

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);

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);

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);

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);

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);

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);

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

Inserts v into the option if it is None, then returns a mutable reference to the contained value.

Examples

#![feature(option_entry)]

let mut x = None;

{
    let y: &mut u32 = x.get_or_insert(5);
    assert_eq!(y, &5);

    *y = 7;
}

assert_eq!(x, Some(7));

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

Inserts a value computed from f into the option if it is None, then returns a mutable reference to the contained value.

Examples

#![feature(option_entry)]

let mut x = None;

{
    let y: &mut u32 = x.get_or_insert_with(|| 5);
    assert_eq!(y, &5);

    *y = 7;
}

assert_eq!(x, Some(7));

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);

impl<'a, T> Option<&'a T> where T: Clone
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Maps an Option<&T> to an Option<T> by cloning the contents of the option.

Examples

let x = 12;
let opt_x = Some(&x);
assert_eq!(opt_x, Some(&12));
let cloned = opt_x.cloned();
assert_eq!(cloned, Some(12));

impl<T> Option<T> where T: Default
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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<F, T, E> Future for Option<F> where F: Future<Item=T, Error=E>
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The type of value that this future will resolved with if it is successful. Read more

The type of error that this future will resolve with if it fails in a normal fashion. Read more

Query this future to see if its value has become available, registering interest if it is not. Read more

Block the current thread until this future is resolved. Read more

Convenience function for turning this future into a trait object which is also Send. Read more

Map this future's result to a different type, returning a new future of the resulting type. Read more

Map this future's error to a different error, returning a new future. Read more

Map this future's error to any error implementing From for this future's Error, returning a new future. Read more

Chain on a computation for when a future finished, passing the result of the future to the provided closure f. Read more

Execute another future after this one has resolved successfully. Read more

Execute another future if this one resolves with an error. Read more

Waits for either one of two futures to complete. Read more

Waits for either one of two differently-typed futures to complete. Read more

Joins the result of two futures, waiting for them both to complete. Read more

Same as join, but with more futures.

Same as join, but with more futures.

Same as join, but with more futures.

Convert this future into a single element stream. Read more

Flatten the execution of this future when the successful result of this future is itself another future. Read more

Flatten the execution of this future when the successful result of this future is a stream. Read more

Fuse a future such that poll will never again be called once it has completed. Read more

Catches unwinding panics while polling the future. Read more

Create a cloneable handle to this future where all handles will resolve to the same result. Read more

impl Buf for Option<[u8; 1]>
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impl<T> Rand for Option<T> where T: Rand
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impl<T> PartialEq<Option<T>> for Option<T> where T: PartialEq<T>
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This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

impl<T> Debug for Option<T> where T: Debug
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Formats the value using the given formatter.

impl<T> IntoIterator for Option<T>
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Returns a consuming iterator over the possibly contained value.

Examples

let x = Some("string");
let v: Vec<&str> = x.into_iter().collect();
assert_eq!(v, ["string"]);

let x = None;
let v: Vec<&str> = x.into_iter().collect();
assert!(v.is_empty());

impl<'a, T> IntoIterator for &'a Option<T>
1.4.0
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impl<'a, T> IntoIterator for &'a mut Option<T>
1.4.0
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impl<T> Eq for Option<T> where T: Eq
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impl<T> Hash for Option<T> where T: Hash
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Feeds this value into the state given, updating the hasher as necessary.

Feeds a slice of this type into the state provided.

impl<A, V> FromIterator<Option<A>> for Option<V> where V: FromIterator<A>
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Takes each element in the Iterator: if it is None, no further elements are taken, and the None is returned. Should no None occur, a container with the values of each Option is returned.

Here is an example which increments every integer in a vector, checking for overflow:

use std::u16;

let v = vec![1, 2];
let res: Option<Vec<u16>> = v.iter().map(|&x: &u16|
    if x == u16::MAX { None }
    else { Some(x + 1) }
).collect();
assert!(res == Some(vec![2, 3]));

impl<T> From<T> for Option<T>
1.12.0
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impl<T> Copy for Option<T> where T: Copy
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impl<T> Ord for Option<T> where T: Ord
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impl<T> Clone for Option<T> where T: Clone
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Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl<T> Default for Option<T>
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Returns None.

impl<T> PartialOrd<Option<T>> for Option<T> where T: PartialOrd<T>
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impl<T> Value for Option<T> where T: Value

impl<T> Serialize for Option<T> where T: Serialize
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Serialize this value into the given Serde serializer. Read more

impl<T> Deserialize for Option<T> where T: Deserialize
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Deserialize this value from the given Serde deserializer. Read more