Struct Argument 

pub struct Argument {
    pub config: ParameterConfig,
    pub default_value: Option<String>,
    /* private fields */
}

A positional command-line argument.

Arguments are positional parameters that appear without dashes. Unlike options, they are required by default and have a single name (no aliases).

Key Differences from Options

• Arguments are positional (no -- prefix)
• Required by default (unless a default is provided)
• Single name only (no short/long aliases)
• Name is displayed in uppercase in help text

Example

use click::argument::Argument;
use click::parameter::Parameter;

// Required argument
let filename = Argument::new("filename").build();
assert!(filename.required());

// Optional argument with default
let output = Argument::new("output")
    .default("out.txt")
    .build();
assert!(!output.required());

Fields

config: ParameterConfig

Parameter configuration.

default_value: Option<String>

The default value (if any).

Implementations

impl Argument

pub fn new(name: &str) -> ArgumentBuilder

Create a new argument builder with the given name.

Example

use click::argument::Argument;

let arg = Argument::builder("filename")
    .help("The file to process")
    .required(true)
    .build();

pub fn builder(name: &str) -> ArgumentBuilder

Alias for new() - create a new argument builder.

pub fn type_converter(&self) -> &dyn AnyTypeConverter

Get the type converter for this argument.

pub fn convert_any( &self, value: &str, ) -> Result<Box<dyn Any + Send + Sync>, String>

Convert a string value using this argument’s type converter. Returns the converted value as a boxed Any type.

pub fn convert(&self, value: &str) -> Result<String, String>

Convert a string value using this argument’s type converter. This is a convenience method that attempts to downcast to String. For non-String types, use convert_any instead.

pub fn get_completions( &self, ctx: &Context, incomplete: &str, ) -> Vec<CompletionItem>

Get shell completions for this argument.

If a custom shell_complete callback is set, it will be used. Otherwise, completions from the type converter are returned.

pub fn has_shell_complete_callback(&self) -> bool

Check if this argument has a custom shell_complete callback.

pub fn default_value(&self) -> Option<&str>

Get the default value for this argument.

pub fn make_metavar(&self) -> String

Generate the metavar for this argument (used in help text).

The metavar is formatted according to Click’s conventions:

• Custom metavar if set, otherwise uppercase name
• Wrapped in [] if optional
• Suffixed with ... if variadic or multiple
• Suffixed with ! if deprecated

Note: Unlike options, arguments use their name (uppercase) by default, not the type’s metavar. This matches Python Click’s behavior.

Trait Implementations

impl Debug for Argument

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

Formats the value using the given formatter.

impl Parameter for Argument

fn name(&self) -> &str

The primary name of the parameter.

fn human_readable_name(&self) -> String

Human-readable name for errors and help text.

fn nargs(&self) -> Nargs

Number of arguments this parameter consumes.

fn multiple(&self) -> bool

Whether this parameter can be specified multiple times.

fn is_eager(&self) -> bool

Whether this parameter should be processed before others.

fn expose_value(&self) -> bool

Whether this parameter’s value should be exposed in ctx.params.

fn required(&self) -> bool

Whether this parameter is required.

fn envvar(&self) -> Option<&[String]>

Get environment variable name(s) for this parameter.

fn help(&self) -> Option<&str>

Get help text for this parameter.

fn hidden(&self) -> bool

Whether this parameter is hidden from help.

fn get_metavar(&self) -> Option<String>

Get the metavar for help text (e.g., “FILE”, “TEXT”).

fn get_help_record(&self) -> Option<(String, String)>

Generate help record for formatting.

fn param_type_name(&self) -> &str

Get the parameter type name (for error messages).