Enum UnknownFlags 

pub enum UnknownFlags {
    Value,
    Error,
}

What to do with a token that looks like a flag but names no declared flag.

The default is UnknownFlags::Value, which is where this parser parts company with clap, argparse, commander, oclif v2+, and POSIX getopt — all of which reject the token. The reason is that those parse their own argv, where a dash-word can only be a flag or a typo, while a usage spec is also used to parse things whose flags it does not own:

• a shell script run through usage exec, forwarding options to a tool it wraps
• a task’s arguments, where the task script is the authority on what it accepts
• a completion, asked about a command line that is still being typed

In all three, a dash-word the spec has not heard of is far more likely to be data in transit than a mistake, and rejecting it would break the wrapper for everyone who did not enumerate the flags of the program behind it.

The cost is real and worth stating: a misspelled --hekp becomes an argument instead of an error, and whether it does depends on whether a positional is free to take it. A CLI that owns all of its flags — as opposed to forwarding them — should say UnknownFlags::Error and get the stricter reading.

Variants

Value

Offer the token to the positional arguments, like any other word. If none can take it, it is an unexpected argument — the same error an extra word would produce.

Error

Reject the token. A CLI whose flags are all its own gets typo detection this way, at the price of needing -- to pass a value that begins with a dash.

Implementations

impl UnknownFlags

pub fn as_str(&self) -> &'static str

Trait Implementations

impl Clone for UnknownFlags

fn clone(&self) -> UnknownFlags

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for UnknownFlags

impl Debug for UnknownFlags

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

Formats the value using the given formatter.

impl Default for UnknownFlags

fn default() -> UnknownFlags

Returns the “default value” for a type.

impl Display for UnknownFlags

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

Formats the value using the given formatter.

impl Eq for UnknownFlags

impl FromStr for UnknownFlags

type Err = ParseError

The associated error which can be returned from parsing.

fn from_str(s: &str) -> Result<UnknownFlags, <Self as FromStr>::Err>

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

impl PartialEq for UnknownFlags

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

Equality operator ==.

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

Inequality operator !=.

impl Serialize for UnknownFlags

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for UnknownFlags

impl TryFrom<&str> for UnknownFlags

type Error = ParseError

The type returned in the event of a conversion error.

fn try_from(s: &str) -> Result<UnknownFlags, <Self as TryFrom<&str>>::Error>

Performs the conversion.