Struct OptionMonoid 

pub struct OptionMonoid<T: Semigroup>(pub Option<T>);

Available on crate feature monoid only.

Construct Monoid from optional Semigroup. Some Semigroup lack a suitable identity element for extension to a Monoid.

Examples

In Semigroup operations of crate::op::Min and crate::op::Max, std::time::Instant does not have a suitable identity element for extension to a Monoid.

use std::time::{Duration, Instant};
use semigroup::{Semigroup, Monoid, OptionMonoid};

#[derive(Debug, Clone, PartialEq, Semigroup)]
#[semigroup(monoid, commutative)]
pub struct BoundingDuration {
    #[semigroup(with = "semigroup::op::Min")]
    start: Instant,
    #[semigroup(with = "semigroup::op::Max")]
    end: Instant,
}
impl BoundingDuration {
     pub fn duration(&self) -> Duration {
        self.end - self.start
    }
}

In such case, OptionMonoid is useful.

use std::time::{Duration, Instant};
use semigroup::{Semigroup, Monoid, OptionMonoid};

#[derive(Debug, Clone, PartialEq, Semigroup)]
#[semigroup(commutative)]
pub struct BoundingDuration {
    #[semigroup(with = "semigroup::op::Min")]
    start: Instant,
    #[semigroup(with = "semigroup::op::Max")]
    end: Instant,
}
impl BoundingDuration {
     pub fn duration(&self) -> Duration {
        self.end - self.start
    }
}

let (now, mut bd) = (Instant::now(), OptionMonoid::unit());
let v = vec! [
    OptionMonoid::from(BoundingDuration { start: now + Duration::from_millis(50), end: now + Duration::from_millis(100) }),
    OptionMonoid::from(BoundingDuration { start: now + Duration::from_millis(100), end: now + Duration::from_millis(200) }),
    OptionMonoid::from(BoundingDuration { start: now + Duration::from_millis(150), end: now + Duration::from_millis(300) }),
];
for vi in v {
    bd = bd.semigroup(vi);
}
assert_eq!(bd.as_ref().unwrap().duration(), Duration::from_millis(250));

Tuple Fields

0: Option<T>

Methods from Deref<Target = Option<T>>

pub 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);

pub 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);

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

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

Examples

Calculates the length of an Option<String> as an Option<usize> without moving the String. 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 text: Option<String> = Some("Hello, world!".to_string());
// First, cast `Option<String>` to `Option<&String>` with `as_ref`,
// then consume *that* with `map`, leaving `text` on the stack.
let text_length: Option<usize> = text.as_ref().map(|s| s.len());
println!("still can print text: {text:?}");

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

Converts from &mut 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));

pub fn as_pin_ref(self: Pin<&Option<T>>) -> Option<Pin<&T>>

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

pub fn as_pin_mut(self: Pin<&mut Option<T>>) -> Option<Pin<&mut T>>

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

pub fn as_slice(&self) -> &[T]

Returns a slice of the contained value, if any. If this is None, an empty slice is returned. This can be useful to have a single type of iterator over an Option or slice.

Note: Should you have an Option<&T> and wish to get a slice of T, you can unpack it via opt.map_or(&[], std::slice::from_ref).

Examples

assert_eq!(
    [Some(1234).as_slice(), None.as_slice()],
    [&[1234][..], &[][..]],
);

The inverse of this function is (discounting borrowing) [_]::first:

for i in [Some(1234_u16), None] {
    assert_eq!(i.as_ref(), i.as_slice().first());
}

pub fn as_mut_slice(&mut self) -> &mut [T]

Returns a mutable slice of the contained value, if any. If this is None, an empty slice is returned. This can be useful to have a single type of iterator over an Option or slice.

Note: Should you have an Option<&mut T> instead of a &mut Option<T>, which this method takes, you can obtain a mutable slice via opt.map_or(&mut [], std::slice::from_mut).

Examples

assert_eq!(
    [Some(1234).as_mut_slice(), None.as_mut_slice()],
    [&mut [1234][..], &mut [][..]],
);

The result is a mutable slice of zero or one items that points into our original Option:

let mut x = Some(1234);
x.as_mut_slice()[0] += 1;
assert_eq!(x, Some(1235));

The inverse of this method (discounting borrowing) is [_]::first_mut:

assert_eq!(Some(123).as_mut_slice().first_mut(), Some(&mut 123))

pub fn as_deref(&self) -> Option<&<T as Deref>::Target>

where T: Deref,

Converts from Option<T> (or &Option<T>) to Option<&T::Target>.

Leaves the original Option in-place, creating a new one with a reference to the original one, additionally coercing the contents via Deref.

Examples

let x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref(), Some("hey"));

let x: Option<String> = None;
assert_eq!(x.as_deref(), None);

pub fn as_deref_mut(&mut self) -> Option<&mut <T as Deref>::Target>

where T: DerefMut,

Converts from Option<T> (or &mut Option<T>) to Option<&mut T::Target>.

Leaves the original Option in-place, creating a new one containing a mutable reference to the inner type’s Deref::Target type.

Examples

let mut x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref_mut().map(|x| {
    x.make_ascii_uppercase();
    x
}), Some("HEY".to_owned().as_mut_str()));

pub 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);

pub 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);

pub fn insert(&mut self, value: T) -> &mut T

Inserts value into the option, then returns a mutable reference to it.

If the option already contains a value, the old value is dropped.

See also Option::get_or_insert, which doesn’t update the value if the option already contains Some.

Example

let mut opt = None;
let val = opt.insert(1);
assert_eq!(*val, 1);
assert_eq!(opt.unwrap(), 1);
let val = opt.insert(2);
assert_eq!(*val, 2);
*val = 3;
assert_eq!(opt.unwrap(), 3);

pub fn get_or_insert(&mut self, value: T) -> &mut T

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

See also Option::insert, which updates the value even if the option already contains Some.

Examples

let mut x = None;

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

    *y = 7;
}

assert_eq!(x, Some(7));

pub fn get_or_insert_default(&mut self) -> &mut T

where T: Default,

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

Examples

let mut x = None;

{
    let y: &mut u32 = x.get_or_insert_default();
    assert_eq!(y, &0);

    *y = 7;
}

assert_eq!(x, Some(7));

pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut T

where F: FnOnce() -> T,

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

Examples

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));

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

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

pub fn take_if<P>(&mut self, predicate: P) -> Option<T>

where P: FnOnce(&mut T) -> bool,

Takes the value out of the option, but only if the predicate evaluates to true on a mutable reference to the value.

In other words, replaces self with None if the predicate returns true. This method operates similar to Option::take but conditional.

Examples

let mut x = Some(42);

let prev = x.take_if(|v| if *v == 42 {
    *v += 1;
    false
} else {
    false
});
assert_eq!(x, Some(43));
assert_eq!(prev, None);

let prev = x.take_if(|v| *v == 43);
assert_eq!(x, None);
assert_eq!(prev, Some(43));

pub fn replace(&mut self, value: T) -> Option<T>

Replaces the actual value in the option by the value given in parameter, returning the old value if present, leaving a Some in its place without deinitializing either one.

Examples

let mut x = Some(2);
let old = x.replace(5);
assert_eq!(x, Some(5));
assert_eq!(old, Some(2));

let mut x = None;
let old = x.replace(3);
assert_eq!(x, Some(3));
assert_eq!(old, None);

Trait Implementations

impl<T: AnnotatedSemigroup<A> + Annotate<A>, A> Annotate<Option<A>> for OptionMonoid<T>

type Annotation = <T as Annotate<A>>::Annotation

fn annotated(self, annotation: Self::Annotation) -> Annotated<Self, Option<A>>

impl<T: AnnotatedSemigroup<A>, A> AnnotatedMonoid<Option<A>> for OptionMonoid<T>

fn annotated_unit() -> Annotated<Self, Option<A>>

impl<T: AnnotatedSemigroup<A>, A> AnnotatedSemigroup<Option<A>> for OptionMonoid<T>

fn annotated_op( base: Annotated<Self, Option<A>>, other: Annotated<Self, Option<A>>, ) -> Annotated<Self, Option<A>>

impl<T: Clone + Semigroup> Clone for OptionMonoid<T>

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

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Semigroup> Construction<Option<T>> for OptionMonoid<T>

fn into_inner(self) -> Option<T>

Convert into inner type of new type struct.

fn lift_op(base: T, other: T) -> T

Semigroup operation between base and other with constructed type. When T does not implement crate::Semigroup, this function can be used.

impl<T: Semigroup> ConstructionMonoid<Option<T>> for OptionMonoid<T>

where Self: Monoid,

fn lift_unit() -> T

Get monoid identity element with constructed type. When T does not implement crate::Monoid, this function can be used.

impl<T: Debug + Semigroup> Debug for OptionMonoid<T>

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

Formats the value using the given formatter.

impl<T: Default + Semigroup> Default for OptionMonoid<T>

fn default() -> OptionMonoid<T>

Returns the “default value” for a type.

impl<T: Semigroup> Deref for OptionMonoid<T>

type Target = Option<T>

The resulting type after dereferencing.

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

Dereferences the value.

impl<T: Semigroup> DerefMut for OptionMonoid<T>

fn deref_mut(&mut self) -> &mut Self::Target

Mutably dereferences the value.

impl<T: Semigroup> From<Option<T>> for OptionMonoid<T>

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

Converts to this type from the input type.

impl<T: Semigroup> From<T> for OptionMonoid<T>

fn from(value: T) -> Self

Converts to this type from the input type.

impl<T: Hash + Semigroup> Hash for OptionMonoid<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<T: Semigroup> Monoid for OptionMonoid<T>

fn unit() -> Self

impl<T: Ord + Semigroup> Ord for OptionMonoid<T>

fn cmp(&self, other: &OptionMonoid<T>) -> 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<T: PartialEq + Semigroup> PartialEq for OptionMonoid<T>

fn eq(&self, other: &OptionMonoid<T>) -> 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<T: PartialOrd + Semigroup> PartialOrd for OptionMonoid<T>

fn partial_cmp(&self, other: &OptionMonoid<T>) -> 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: Semigroup> Semigroup for OptionMonoid<T>

fn op(base: Self, other: Self) -> Self

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

where Self: Sized,

impl<T: Copy + Semigroup> Copy for OptionMonoid<T>

impl<T: Eq + Semigroup> Eq for OptionMonoid<T>

impl<T: Semigroup> StructuralPartialEq for OptionMonoid<T>