Struct proc_macro_kwargs::parse::ExplicitOption

pub struct ExplicitOption<T>(pub Option<T>);

A version of Option that is parsed with explicit Some(<inner>) or None syntax

This is as opposed to a regular Option, which requires no extra syntax and always parses to Some (it’s intended for use with optional args)

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_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_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 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);

Trait Implementations

impl<T: Clone> Clone for ExplicitOption<T>

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

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for ExplicitOption<T>

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

Formats the value using the given formatter.

impl<T> Deref for ExplicitOption<T>

type Target = Option<T>

The resulting type after dereferencing.

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

Dereferences the value.

impl<T> From<ExplicitOption<T>> for Option<T>

fn from(explicit: ExplicitOption<T>) -> Option<T>

Converts to this type from the input type.

impl<T> From<Option<T>> for ExplicitOption<T>

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

Converts to this type from the input type.

impl<T: Hash> Hash for ExplicitOption<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: MacroArg> MacroArg for ExplicitOption<T>

fn parse_macro_arg(stream: ParseStream<'_>) -> Result<Self>

Parse the argument to the macro

impl<T: PartialEq> PartialEq for ExplicitOption<T>

fn eq(&self, other: &ExplicitOption<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: Copy> Copy for ExplicitOption<T>

impl<T: Eq> Eq for ExplicitOption<T>

impl<T> StructuralPartialEq for ExplicitOption<T>