Argument Types Reference

This page lists every argument type clish supports, along with behavior details and compile-time restrictions.

Type table

Type	Kind	Required?	Behavior	Example invocation
Pos<T>	Positional	Yes	Reads the next positional value	myapp cmd foo
Pos<Option<T>>	Positional	No	Reads the next positional value if available	myapp cmd or myapp cmd foo
Pos<Vec<T>>	Positional	No (zero or more)	Reads all remaining positional values	myapp cmd a b c
Named<T>	Named option	Yes	Reads the value after --name	myapp cmd --env prod
Named<Option<T>>	Named option	No	Reads the value after --name if provided
Named<Vec<T>>	Named option	No (repeatable)	Collects all values for --name	myapp cmd --tag a --tag b
bool	Flag	No	True if --name is present, false otherwise	myapp cmd --force

Type parameter constraints

The inner type T must implement FromStr. Built-in types that work include:

Type	Description
String	Any text
i8, i16, i32, i64, i128	Signed integers
u8, u16, u32, u64, u128	Unsigned integers
f32, f64	Floating point numbers
bool	Boolean (parsed from "true"/"false")
PathBuf	File system path
Custom types	Any type implementing FromStr

Parse failures produce a runtime error:

error: invalid value 'abc': expected u16
  |
1 | myapp serve --port abc
  |                    ^^^
  |
  = hint: run 'myapp serve --help' for more information

Compile-time restrictions

The following type combinations are rejected at compile time:

Rejected type	Reason	Fix
Option<Vec<T>>	Vec<T> already accepts zero or more values	Use Vec<T>
Option<bool>	Flags are already optional by presence	Use bool
Multiple Pos<Vec<T>>	Only one variadic positional is allowed per command	Use a single Pos<Vec<T>>
Pos<Vec<T>> not last	Variadic must consume all remaining positionals	Move it to the last positional position

Named option syntax

Named options support several input forms:

Form	Example
--name value	--env production
--name=value	--env=production
-n value (with short alias)	-e production
-nvalue (with short alias)	-eproduction

Flag syntax

Flags support these forms:

Form	Example
--flag	--force
-f (with short alias)	-f
Bundled short flags	-vf (equivalent to -v -f)

When bundling short flags, only flags (not options) can be combined. If a short option appears in a bundle, the parser stops and reports that the option is missing its value.

Positional argument separator

Use -- to signal that all following arguments are positional, even if they look like flags:

myapp process -- -file.txt --not-a-flag

Everything after -- is treated as a positional value.