`class One`

Represents a single positional argument in a command.

A One parser extracts exactly one argument from the command line that matches the specified pattern.

Definitions

`def initialize(key, description, pattern: //, default: nil, required: false)`

Initialize a new positional argument parser.

Signature

parameter　key　Symbol: The name of the attribute to store the value in.
parameter　description　String: A description of the argument for help output.
parameter　pattern　Regexp: A pattern to match valid values.
parameter　default　Object: The default value if no argument is provided.
parameter　required　Boolean: Whether the argument is required.

Implementation

def initialize(key, description, pattern: //, default: nil, required: false)
	@key = key
	@description = description
	@pattern = pattern
	@default = default
	@required = required
end

`attr :key`

The name of the attribute to store the value in.

Signature

attribute　Symbol

`attr :description`

A description of the argument for help output.

Signature

attribute　String

`attr :pattern`

A pattern to match valid values.

Signature

attribute　Regexp

`attr :default`

The default value if no argument is provided.

Signature

attribute　Object

`attr :required`

Whether the argument is required.

Signature

attribute　Boolean

`def to_s`

Generate a string representation for usage output.

Signature

returns　String: The usage string.

Implementation

def to_s
	"<#{@key}>"
end

`def to_a`

Generate an array representation for usage output.

Signature

returns　Array: The usage array.

Implementation

def to_a
	usage = [to_s, @description]
	
	if @default
		usage << "(default: #{@default.inspect})"
	elsif @required
		usage << "(required)"
	end
	
	return usage
end

`def parse(input, parent = nil, default = nil)`

Parse a single argument from the input.

Signature

parameter　input　Array(String): The command-line arguments.
parameter　parent　Command | Nil: The parent command.
parameter　default　Object | Nil: An override for the default value.
returns　String | Object | Nil: The parsed value, or the default if no match.

Implementation

def parse(input, parent = nil, default = nil)
	if input.first =~ @pattern
		input.shift
	elsif default ||= @default
		return default
	elsif @required
		raise MissingValueError.new(parent, @key)
	end
end