Enum ParsingError 

pub enum ParsingError {
    InvalidOption {
        reason: &'static str,
        offender: Option<String>,
    },
    UnconsumedValue {
        value: String,
    },
    Empty,
    UnexpectedArg {
        offender: String,
        value: Option<String>,
        format: &'static str,
        prefix: &'static str,
    },
}

Errors that can occur during argument parsing.

All parsing operations return a Result with this error type. Each variant provides specific context about what went wrong during parsing.

Variants

InvalidOption

Invalid option syntax or format was encountered.

This typically occurs when:

• Short options are given values with = syntax (e.g., -x=value)
• Malformed option syntax is detected

Fields

• reason - Human-readable description of what was invalid
• offender - The specific argument that caused the error (if available)

Fields

reason: &'static str

offender: Option<String>

UnconsumedValue

An option value was not consumed after being parsed.

This occurs when a long option has an attached value (e.g., --file=input.txt) but the application doesn’t call Parser::value or Parser::ignore_value before parsing the next argument.

Fields

• value - The unconsumed value that was attached to the option

Fields

value: String

Empty

The argument iterator was empty (contained no program name).

This should not occur during normal program execution but may happen when creating parsers from empty custom iterators.

UnexpectedArg

An unexpected or unrecognized argument was encountered.

This error is typically created by calling Argument::into_error when the application encounters an argument it doesn’t know how to handle.

Fields

• offender - The argument name that was unexpected
• value - Associated value (if any)
• format - How the value is formatted in error messages (e.g., “=” or “ “)
• prefix - The argument prefix (e.g., “–” for long options, “-” for short)

Fields

offender: String

value: Option<String>

format: &'static str

prefix: &'static str

Trait Implementations

impl Debug for ParsingError

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

Formats the value using the given formatter.

impl Display for ParsingError

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

Formats the value using the given formatter.

impl Error for ParsingError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

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

Provides type-based access to context intended for error reports.