Struct Maybe 

pub struct Maybe<T: Pattern>(pub T);

A pattern that matches 0 or 1 occurrences of the inner pattern T, making it optional.

Because both 0 and 1 occurrences are valid matches, Maybe never fails: Pattern::immediate_match and Pattern::trailing_match always return Ok, falling back to an empty match at the relevant end of the input if T doesn’t match there. Likewise, Pattern::first_match / Pattern::first_match_ex always match at the very start of the input.

More conveniently created via Pattern::maybe

Example

use {
    shrimple_parser::{
        Pattern,
        parser::one,
        pattern::Maybe,
    },
    core::convert::Infallible,
};

// Matches an optional '-' sign at the start of the input.
assert_eq!(
    one::<_, Infallible>('-'.maybe())("-123"),
    Ok(("123", "-")),
);

// No '-' present - still matches, with an empty matched fragment.
assert_eq!(
    one::<_, Infallible>('-'.maybe())("123"),
    Ok(("123", "")),
);

Tuple Fields

0: T

Trait Implementations

impl<T: Clone + Pattern> Clone for Maybe<T>

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

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<T: Copy + Pattern> Copy for Maybe<T>

impl<T: Debug + Pattern> Debug for Maybe<T>

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

Formats the value using the given formatter.

impl<T: Pattern> Pattern for Maybe<T>

fn immediate_matches<I: Input>(&self, input: I) -> (I, I)

Repeating “0 or 1 T” is the same as “0 or more T”, so this delegates directly to T’s implementation rather than looping on Pattern::immediate_match, which would never terminate since Maybe::immediate_match never fails.

fn trailing_matches_counted<I: Input>(&self, input: I) -> (I, usize)

See Maybe::immediate_matches for why this delegates straight to T instead of looping on Pattern::trailing_match.

fn immediate_match<I: Input>(&self, input: I) -> Result<(I, I), I>

The return values are (rest of the input, matched fragment at the beginning).

fn immediate_matches_counted<I: Input>(&self, input: I) -> (I, (I, usize))

Like Pattern::immediate_matches, but also counts the number of matches.

fn trailing_match<I: Input>(&self, input: I) -> Result<(I, I), I>

Like Pattern::immediate_match, but matches at the end of input. The return values are (the input before the match, the match)

fn first_match<I: Input>(&self, input: I) -> Result<(I, (I, I)), I>

The return values are (the match + rest of the input, (string before the match, the match)).

fn first_match_ex<I: Input>(&self, input: I) -> Result<(I, (I, I)), I>

Like Pattern::first_match, but the match is excluded from the rest of the input.

fn by_ref(&self) -> Ref<'_, Self>

Get the pattern by reference to avoid moving it, which will happen in generic code

fn and<Other: Pattern>(self, other: Other) -> Chain<Self, Other>

where Self: Sized,

Combine self and another pattern into a pattern that matches both of them in a sequence, with self before other

fn not_escaped_by<Prefix: Pattern>( self, prefix: Prefix, ) -> NotEscaped<Prefix, Self>

where Self: Sized,

Create a pattern that’ll match self only if it’s not escaped (immediately preceded) by the provided pattern.

fn not_enclosed_by<Enclosure: Pattern>( self, enc: Enclosure, ) -> NotEnclosed<Enclosure, Self>

where Self: Sized,

Create a pattern that’ll match self only if it’s not enclosed (preceded & superceded) by the provided pattern.

fn many(self) -> Many<Self>

where Self: Sized,

Creates a greedy pattern that matches self as many times as possible. See Many

fn maybe(self) -> Maybe<Self>

where Self: Sized,

Creates a pattern that matches self 0 or 1 times. See Maybe