Enum Arity 

pub enum Arity {
    None,
    Required,
    Optional,
    LastArgDefault,
}

What: enum Arity lists how an option relates to a value. An enum is a closed set of named alternatives. #[derive(...)] asks the compiler to generate copying (Clone, Copy), debug printing (Debug) and == (Eq, PartialEq). Why: Value consumption decides whether the next token is a path or an option value.

In TS you’d write (pseudocode):

type Arity = 'none' | 'required' | 'optional' | 'last-argument-default';

Variants

None

PARSE_OPT_NOARG: never takes a value; --name=value is an error.

Required

Takes the attached value, otherwise the next token (get_arg, parse-options.c:47-62).

Optional

PARSE_OPT_OPTARG: takes an attached value only, never the next token (203-204).

LastArgDefault

PARSE_OPT_LASTARG_DEFAULT: like Required, but valid without a value when last (54-55).

Trait Implementations

impl Clone for Arity

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Arity

impl Debug for Arity

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

Formats the value using the given formatter.

impl Eq for Arity

impl PartialEq for Arity

fn eq(&self, other: &Self) -> bool

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Arity