Struct parsel::ast::Maybe

pub struct Maybe<P, T = Empty> { /* private fields */ }

Parses an optional expression introduced by some lookahead tokens.

#[derive(PartialEq, Eq, Debug, Parse, ToTokens)]
enum Ty {
    Named(Ident),
    Ref(
        token::And,
        #[parsel(recursive)]
        Box<Self>,
    ),
    Opt(
        token::Question,
        #[parsel(recursive)]
        Box<Self>,
    ),
}

#[derive(PartialEq, Eq, Debug, Parse, ToTokens)]
struct TyAnnot {
    colon: token::Colon,
    ty: Ty,
}

#[derive(PartialEq, Eq, Debug, Parse, ToTokens)]
struct Function {
    kw_fn: token::Fn,
    name: Ident,
    argument: Paren<Maybe<Ident, TyAnnot>>,
    return_ty: Maybe<token::RArrow, Ty>,
    body: Brace<Empty>,
}

let unit_to_unit_function: Function = parse_quote!{
    fn foo() {}
};
assert_eq!(
    unit_to_unit_function,
    Function {
        kw_fn: Default::default(),
        name: ident("foo"),
        argument: Paren::default(),
        return_ty: Maybe::default(),
        body: Brace::default(),
    }
);

let unit_to_opt_function: Function = parse_quote!{
    fn another_name() -> ?Rofl {}
};
assert_eq!(
    unit_to_opt_function,
    Function {
        kw_fn: Default::default(),
        name: ident("another_name"),
        argument: Paren::default(),
        return_ty: Maybe::from((
            token::RArrow::default(),
            Ty::Opt(
                token::Question::default(),
                Box::new(Ty::Named(ident("Rofl"))),
            )
        )),
        body: Brace::default(),
    }
);

let opt_to_ref_function: Function = parse_quote!{
    fn fn_3(the_arg: ?&DoubleTrouble) -> &Indirect {}
};
assert_eq!(
    opt_to_ref_function,
    Function {
        kw_fn: Default::default(),
        name: ident("fn_3"),
        argument: Paren::from(Maybe::from((
            ident("the_arg"),
            TyAnnot {
                colon: Default::default(),
                ty: Ty::Opt(
                    token::Question::default(),
                    Box::new(Ty::Ref(
                        token::And::default(),
                        Box::new(Ty::Named(ident("DoubleTrouble"))),
                    )),
                )
            }
        ))),
        return_ty: Maybe::from((
            token::RArrow::default(),
            Ty::Ref(
                token::And::default(),
                Box::new(Ty::Named(ident("Indirect"))),
            )
        )),
        body: Brace::default(),
    }
);

Implementations

impl<P, T> Maybe<P, T>

pub const fn new() -> Self

pub fn as_prefix(&self) -> Option<&P>

pub fn as_prefix_mut(&mut self) -> Option<&mut P>

pub fn into_prefix(self) -> Option<P>

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

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

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

pub fn as_parts(&self) -> Option<&(P, T)>

pub fn as_parts_mut(&mut self) -> Option<&mut (P, T)>

pub fn into_parts(self) -> Option<(P, T)>

pub fn into_prefix_iter(self) -> IntoIter<P>

pub fn prefix_iter(&self) -> IntoIter<&P>

pub fn prefix_iter_mut(&mut self) -> IntoIter<&mut P>

pub fn iter(&self) -> IntoIter<&T>

pub fn iter_mut(&mut self) -> IntoIter<&mut T>

pub fn into_parts_iter(self) -> IntoIter<(P, T)>

pub fn parts_iter(&self) -> Iter<'_, (P, T)>

pub fn parts_iter_mut(&mut self) -> IterMut<'_, (P, T)>

Methods from Deref<Target = Option<(P, 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,

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

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

Examples

#![feature(option_get_or_insert_default)]

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,

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

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

#![feature(option_take_if)]

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<P: Clone, T: Clone> Clone for Maybe<P, T>

fn clone(&self) -> Maybe<P, T>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<P, T> Debug for Maybe<P, T>

where P: Debug, T: Debug,

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

Formats the value using the given formatter.

impl<P, T> Default for Maybe<P, T>

fn default() -> Self

Returns the “default value” for a type.

impl<P, T> Deref for Maybe<P, T>

type Target = Option<(P, T)>

The resulting type after dereferencing.

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

Dereferences the value.

impl<P, T> DerefMut for Maybe<P, T>

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

Mutably dereferences the value.

impl<P, T> Display for Maybe<P, T>

where P: ToTokens, T: ToTokens,

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

Formats the value using the given formatter.

impl<P, T> From<(P, T)> for Maybe<P, T>

fn from(parts: (P, T)) -> Self

Converts to this type from the input type.

impl<P, T> From<Option<(P, T)>> for Maybe<P, T>

fn from(inner: Option<(P, T)>) -> Self

Converts to this type from the input type.

impl<P: Default, T> From<Option<T>> for Maybe<P, T>

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

Converts to this type from the input type.

impl<P: Default, T> From<T> for Maybe<P, T>

fn from(tail: T) -> Self

Converts to this type from the input type.

impl<P, T> FromStr for Maybe<P, T>

where P: Parse, T: Parse,

type Err = Error

The associated error which can be returned from parsing.

fn from_str(string: &str) -> Result<Self>

Parses a string s to return a value of this type.

impl<P: Hash, T: Hash> Hash for Maybe<P, 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<'a, P, T> IntoIterator for &'a Maybe<P, T>

type Item = &'a T

The type of the elements being iterated over.

type IntoIter = IntoIter<&'a T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<'a, P, T> IntoIterator for &'a mut Maybe<P, T>

type Item = &'a mut T

The type of the elements being iterated over.

type IntoIter = IntoIter<&'a mut T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<P, T> IntoIterator for Maybe<P, T>

type Item = T

The type of the elements being iterated over.

type IntoIter = IntoIter<T>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<P, T> Parse for Maybe<P, T>

where P: Parse, T: Parse,

fn parse(input: ParseStream<'_>) -> Result<Self>

impl<P: PartialEq, T: PartialEq> PartialEq for Maybe<P, T>

fn eq(&self, other: &Maybe<P, 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<P, T> ToTokens for Maybe<P, T>

where P: ToTokens, T: ToTokens,

fn to_tokens(&self, tokens: &mut TokenStream)

Write self to the given TokenStream.

fn to_token_stream(&self) -> TokenStream

Convert self directly into a TokenStream object.

fn into_token_stream(self) -> TokenStream

where Self: Sized,

Convert self directly into a TokenStream object.

impl<P: Copy, T: Copy> Copy for Maybe<P, T>

impl<P: Eq, T: Eq> Eq for Maybe<P, T>

impl<P, T> StructuralPartialEq for Maybe<P, T>