Trait Parameter 

pub trait Parameter:
    Send
    + Sync
    + Debug {
    // Required methods
    fn name(&self) -> &str;
    fn human_readable_name(&self) -> String;
    fn nargs(&self) -> Nargs;
    fn multiple(&self) -> bool;
    fn is_eager(&self) -> bool;
    fn expose_value(&self) -> bool;
    fn required(&self) -> bool;
    fn envvar(&self) -> Option<&[String]>;
    fn help(&self) -> Option<&str>;
    fn hidden(&self) -> bool;
    fn get_metavar(&self) -> Option<String>;
    fn get_help_record(&self) -> Option<(String, String)>;

    // Provided method
    fn param_type_name(&self) -> &str { ... }
}

A trait for command-line parameters (options and arguments).

This trait defines the common interface for all parameter types. Options and Arguments implement this trait with their specific behaviors.

Required Methods

fn name(&self) -> &str

The primary name of the parameter.

For options, this is typically the long option name without dashes. For arguments, this is the argument name.

fn human_readable_name(&self) -> String

Human-readable name for errors and help text.

For options, this is usually the option flags (e.g., “–name / -n”). For arguments, this is typically the metavar in uppercase.

fn nargs(&self) -> Nargs

Number of arguments this parameter consumes.

fn multiple(&self) -> bool

Whether this parameter can be specified multiple times.

When true, the parameter collects values into a list/tuple.

fn is_eager(&self) -> bool

Whether this parameter should be processed before others.

Eager parameters (like --help and --version) are processed first and can short-circuit command execution.

fn expose_value(&self) -> bool

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

When false, the parameter is still processed but its value is not stored in the context parameters.

fn required(&self) -> bool

Whether this parameter is required.

Required parameters must be provided via CLI, environment, or default.

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

Get environment variable name(s) for this parameter.

Returns None if no environment variables are configured. Multiple environment variables can be specified; the first non-empty value is used.

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”).

If not explicitly set, the type’s metavar is used.

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

Generate help record for formatting.

Returns a tuple of (option_string, help_string) for help display, or None if this parameter should not appear in help.

Provided Methods

fn param_type_name(&self) -> &str

Get the parameter type name (for error messages).

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl Parameter for Argument

impl Parameter for ClickOption