Struct darling::util::Flag

pub struct Flag(_);

Marker type equivalent to Option<()> for use in attribute parsing.

Implementations

impl Flag

pub fn present() -> Flag

Creates a new Flag which corresponds to the presence of a value.

Methods from Deref<Target = Option<()>>

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_some_and(&self, f: impl FnOnce(&T) -> bool) -> bool

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

Returns true if the option is a Some and the value inside of it matches a predicate.

Examples

#![feature(is_some_with)]

let x: Option<u32> = Some(2);
assert_eq!(x.is_some_and(|&x| x > 1), true);

let x: Option<u32> = Some(0);
assert_eq!(x.is_some_and(|&x| x > 1), false);

let x: Option<u32> = None;
assert_eq!(x.is_some_and(|&x| x > 1), 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

Converts 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 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_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);

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

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

Returns true if the option is a Some value containing the given value.

Examples

#![feature(option_result_contains)]

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

let x: Option<u32> = Some(3);
assert_eq!(x.contains(&2), false);

let x: Option<u32> = None;
assert_eq!(x.contains(&2), false);

Trait Implementations

impl BitAnd<Flag> for Flag

type Output = Flag

The resulting type after applying the & operator.

fn bitand(self, rhs: Flag) -> Flag

Performs the & operation.

impl BitOr<Flag> for Flag

type Output = Flag

The resulting type after applying the | operator.

fn bitor(self, rhs: Flag) -> Flag

Performs the | operation.

impl Clone for Flag

fn clone(&self) -> Flag

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Flag

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

Formats the value using the given formatter.

impl Default for Flag

fn default() -> Flag

Returns the “default value” for a type.

impl Deref for Flag

type Target = Option<()>

The resulting type after dereferencing.

fn deref(&self) -> &<Flag as Deref>::Target

Dereferences the value.

impl From<Flag> for bool

fn from(flag: Flag) -> bool

Converts to this type from the input type.

impl From<Option<()>> for Flag

fn from(v: Option<()>) -> Flag

Converts to this type from the input type.

impl From<bool> for Flag

fn from(v: bool) -> Flag

Converts to this type from the input type.

impl FromMeta for Flag

fn from_meta(mi: &Meta) -> Result<Flag, Error>

Create an instance from a syn::Meta by dispatching to the format-appropriate trait function. This generally should not be overridden by implementers.

fn from_nested_meta(item: &NestedMeta) -> Result<Self, Error>

fn from_word() -> Result<Self, Error>

Create an instance from the presence of the word in the attribute with no additional options specified.

fn from_list(items: &[NestedMeta]) -> Result<Self, Error>

Create an instance from a list of nested meta items.

fn from_value(value: &Lit) -> Result<Self, Error>

Create an instance from a literal value of either foo = "bar" or foo("bar"). This dispatches to the appropriate method based on the type of literal encountered, and generally should not be overridden by implementers.

fn from_char(value: char) -> Result<Self, Error>

Create an instance from a char literal in a value position.

fn from_string(value: &str) -> Result<Self, Error>

Create an instance from a string literal in a value position.

fn from_bool(value: bool) -> Result<Self, Error>

Create an instance from a bool literal in a value position.

impl Not for Flag

type Output = Flag

The resulting type after applying the ! operator.

fn not(self) -> Flag

Performs the unary ! operation.

impl PartialEq<Flag> for Flag

fn eq(&self, other: &Flag) -> 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 PartialEq<Flag> for Option<()>

fn eq(&self, rhs: &Flag) -> 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 PartialEq<Option<()>> for Flag

fn eq(&self, rhs: &Option<()>) -> 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 PartialEq<bool> for Flag

fn eq(&self, rhs: &bool) -> 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 Copy for Flag

impl Eq for Flag

impl StructuralEq for Flag

impl StructuralPartialEq for Flag