Enum optional_field::Field

pub enum Field<T> {
    Missing,
    Present(Option<T>),
}

Variants

Missing

Present(Option<T>)

Implementations

impl<T> Field<T>

pub fn is_missing(&self) -> bool

Is the value missing?

Examples

assert!(Missing::<u8>.is_missing());
assert!(!Present::<u8>(None).is_missing());
assert!(!Present(Some(1)).is_missing());

pub fn is_present(&self) -> bool

Is the value present?

Examples

assert!(!Missing::<u8>.is_present());
assert!(Present::<u8>(None).is_present());
assert!(Present(Some(1)).is_present());

pub fn has_value(&self) -> bool

Is present and the value is not None?

Examples

assert!(!Missing::<u8>.has_value());
assert!(!Present::<u8>(None).has_value());
assert!(Present(Some(1)).has_value());

pub fn contains<U>(&self, x: &U) -> boolwhere
    U: PartialEq<T>,

Does the value contain the given value?

Examples

let x = 1;
assert!(!Missing::<u8>.contains(&x));
assert!(!Present::<u8>(None).contains(&x));
assert!(Present(Some(1)).contains(&x));

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

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

Examples

Converts a Field<String> into an Field<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 Field to a reference to the value inside the original.

let text: Field<String> = Present(Some("Hello, world!".to_string()));
// First, cast `Field<String>` to `Field<&String>` with `as_ref`,
// then consume *that* with `map`, leaving `text` on the stack.
let text_length: Field<usize> = text.as_ref().map(|s| s.len());
println!("still can print text: {:?}", text);

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

Converts from &mut Field<T> to Field<&mut T>.

Examples

let mut x = Present(Some(2));
match x.as_mut() {
    Present(Some(v)) => *v = 42,
    _ => {},
}
assert_eq!(x, Present(Some(42)));

pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Field<U>

Maps a Field<T> to Field<U> by applying a function to the value contained in the inner Option.

Examples

Converts a Field<String> into an Field<usize>, consuming the original:

let maybe_some_string = Present(Some(String::from("Hello, World!")));
// `Field::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, Present(Some(13)));

pub fn map_present<U, F: FnOnce(Option<T>) -> Option<U>>(self, f: F) -> Field<U>

Maps a Field<T> to Field<U> by applying a function to the option contained in Present.

Examples

Converts a Field<String> into an Field<usize>, consuming the original:

let maybe_some_string = Present(Some(String::from("Hello, World!")));
// `Field::map_present` takes self *by value*, consuming `maybe_some_string`
let maybe_some_len = maybe_some_string.map_present(|s| None);

assert_eq!(maybe_some_len, Present::<usize>(None));

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

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

Arguments passed to map_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use map_or_else, which is lazily evaluated.

Examples

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

let x: Field<&str> = Missing;
assert_eq!(x.map_or(42, |v| v.len()), 42);

pub fn map_present_or<U, F: FnOnce(Option<T>) -> Option<U>>(
    self,
    default: Option<U>,
    f: F
) -> Option<U>

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

Examples

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

let x: Field<&str> = Missing;
assert_eq!(x.map_or(42, |v| v.len()), 42);

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

Computes a default function result if the field is Missing or Present(None), or applies a different function to the contained value (if any).

Examples

let k = 21;

let x = Present(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);

pub fn map_present_or_else<U, D: FnOnce() -> Option<U>, F: FnOnce(Option<T>) -> Option<U>>(
    self,
    default: D,
    f: F
) -> Option<U>

Computes a default function result (if missing), or applies a different function to the contained value (if any).

Examples

let k = 21;

let x = Present(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);

pub fn unwrap(self) -> T

Returns the contained Some value, consuming the self value.

Panics

Panics if the self value equals Missing or Present(None).

Examples

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

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

pub fn unwrap_present(self) -> Option<T>

Returns the contained option, consuming the self value.

Panics

Panics if the self value equals Missing.

Examples

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

let x: Field<&str> = Missing;
assert_eq!(x.unwrap(), "air"); // fails

pub fn unwrap_or(self, default: T) -> T

Returns the contained Some value or a provided default.

Arguments passed to unwrap_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use unwrap_or_else, which is lazily evaluated.

Examples

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

pub fn unwrap_present_or(self, default: Option<T>) -> Option<T>

Returns the contained Present value or a provided default.

Examples

assert_eq!(Present(Some("car")).unwrap_present_or(Some("bike")), Some("car"));
assert_eq!(Present(None).unwrap_present_or(Some("bike")), None);
assert_eq!(Missing.unwrap_present_or(Some("bike")), Some("bike"));

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

Returns the contained Some value or computes it from a closure.

Examples

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

pub fn unwrap_present_or_else<F: FnOnce() -> Option<T>>(self, f: F) -> Option<T>

Returns the contained Present value or computes it from a closure.

Examples

assert_eq!(Present(Some(4)).unwrap_present_or_else(|| Some(10)), Some(4));
assert_eq!(Present(None).unwrap_present_or_else(|| Some(20)), None);
assert_eq!(Missing.unwrap_present_or_else(|| Some(30)), Some(30));

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

Returns the contained Some value from within Present, consuming the self value.

Panics

Panics if the value is a Missing or [‘None’] with a custom panic message provided by msg.

Examples

let x = Present(Some("value"));
assert_eq!(x.expect("fruits are healthy"), "value");

let x: Field<Option<&str>> = Missing;
x.expect("fruits are healthy"); // panics with `fruits are healthy`

pub fn expect_present(self, msg: &str) -> Option<T>

Returns the contained Option in the Present, consuming the self value.

Panics

Panics if the value is a Missing with a custom panic message provided by msg.

Examples

let x: Field<Option<&str>> = Present(None);
assert_eq!(x.expect_present("fruits are healthy"), None);

let x: Field<Option<&str>> = Missing;
x.expect("fruits are healthy"); // panics with `fruits are healthy`

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

pub fn ok_present_or<E>(self, err: E) -> Result<Option<T>, E>

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

pub fn ok_present_or_else<E, F: FnOnce() -> E>(
    self,
    err: F
) -> Result<Option<T>, E>

impl<T: Default> Field<T>

pub fn unwrap_or_default(self) -> T

pub fn unwrap_present_or_default(self) -> Option<T>

impl<T: Copy> Field<&T>

pub fn copied(self) -> Field<T>

Maps a Field<&T> to a Field<T> by copying the contents of the option.

Examples

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

impl<T: Copy> Field<&mut T>

pub fn copied(self) -> Field<T>

Maps a Field<&mut T> to an Field<T> by copying the contents of the option.

Examples

let mut x = 12;
let opt_x = Present(Some(&x));
assert_eq!(opt_x, Present(Some(&x)));
let copied = opt_x.copied();
assert_eq!(copied, Present(Some(12)));

impl<T: Clone> Field<&T>

pub fn cloned(self) -> Field<T>

Maps a Field<&T> to a Field<T> by cloning the contents .

Examples

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

impl<T: Clone> Field<&mut T>

pub fn cloned(self) -> Field<T>

Maps a Field<&mut T> to a Field<T> by cloning the contents.

Examples

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

impl<T: Deref> Field<T>

pub fn as_deref(&self) -> Field<&T::Target>

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

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

Examples

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

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

impl<T: DerefMut> Field<T>

pub fn as_deref_mut(&mut self) -> Field<&mut T::Target>

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

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

Examples

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

impl<T> Field<T>where
    T: Clone + PartialEq,

pub fn delta(&self, other: &Field<T>) -> Field<T>

Returns a new Field which is the difference between Self and other.

Assumes Self is the current value and other is the “new” value, it evaluates if the value has changed and if so returns a field with the new value.

Examples

let old = Present(Some("oh hai"));
// Values are the same
assert_eq!(Missing, old.delta(&Present(Some("oh hai"))));
// There is no new value to compare
assert_eq!(Missing, old.delta(&Missing));
// The value has changed
assert_eq!(Present(Some("new")), old.delta(&Present(Some("new"))));

Trait Implementations

impl<T: Clone> Clone for Field<T>

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

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for Field<T>

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

Formats the value using the given formatter.

impl<T> Default for Field<T>

fn default() -> Self

Returns the “default value” for a type.

impl<'de, T> Deserialize<'de> for Field<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> From<Option<Option<T>>> for Field<T>

fn from(opt: Option<Option<T>>) -> Field<T>

Converts to this type from the input type.

impl<T> From<Option<T>> for Field<T>

fn from(opt: Option<T>) -> Field<T>

Converts to this type from the input type.

impl<T> From<T> for Field<T>

fn from(val: T) -> Field<T>

Converts to this type from the input type.

impl<T: PartialEq> PartialEq<Field<T>> for Field<T>

fn eq(&self, other: &Field<T>) -> bool

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

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

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T> Serialize for Field<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: Eq> Eq for Field<T>

impl<T> StructuralEq for Field<T>

impl<T> StructuralPartialEq for Field<T>