Optionnal options

Options are named parameters.

By default:

• an attribute is mapped to an option if it has a default value,
• and as it has a default value, it is optional

We will see in the next page how this can be changed.

An implicit option

First, we add an option to our command:

require "clip"

module Myapplication
  VERSION = "0.1.0"

  struct Command
    include Clip::Mapper

    getter repeat = 1
    getter name : String
  end

  def self.run
    begin
      command = Command.parse
    rescue ex : Clip::Error
      puts ex
      return
    end

    if command.is_a?(Clip::Mapper::Help)
      puts command.help
    else
      hello(command.name, command.repeat)
    end
  end

  def self.hello(name, repeat)
    repeat.times { puts "Hello #{name}" }
  end
end

Myapplication.run

Tip

We don't have to specify the type of the attribute repeat, as the compiler will infer from the default value 1 that it is an Int32.

Let's try our option:

$ shards build
Dependencies are satisfied
Building: myapplication
$ ./bin/myapplication --help
Usage: ./bin/myapplication [OPTIONS] NAME

Arguments:
  NAME  [required]

Options:
  --repeat INTEGER  [default: 1]
  --help            Show this message and exit.
$ ./bin/myapplication Alice
Hello Alice
$ ./bin/myapplication --repeat 2 Alice
Hello Alice
Hello Alice

It all works as expected: the option --repeat is optional and has a default value.

We can also use an = character to define the value:

$ ./bin/myapplication --repeat=2 Alice
Hello Alice
Hello Alice

An explicit option

An option can be explicitly declared with the annotation Clip::Option.

require "clip"

module Myapplication
  VERSION = "0.1.0"

  struct Command
    include Clip::Mapper

    @[Clip::Option]
    getter repeat = 1
    getter name : String
  end

  def self.run
    begin
      command = Command.parse
    rescue ex : Clip::Error
      puts ex
      return
    end

    if command.is_a?(Clip::Mapper::Help)
      puts command.help
    else
      hello(command.name, command.repeat)
    end
  end

  def self.hello(name, repeat)
    repeat.times { puts "Hello #{name}" }
  end
end

Myapplication.run

Nothing has changed:

$ shards build
Dependencies are satisfied
Building: myapplication
$ ./bin/myapplication --help
Usage: ./bin/myapplication [OPTIONS] NAME

Arguments:
  NAME  [required]

Options:
  --repeat INTEGER  [default: 1]
  --help            Show this message and exit.
$ ./bin/myapplication Alice
Hello Alice
$ ./bin/myapplication --repeat 2 Alice
Hello Alice
Hello Alice