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EXTEND_IRB.md

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Extend IRB

From v1.13.0, IRB provides official APIs to extend its functionality. This feature allows libraries to customize and enhance their users' IRB sessions by adding new commands and helper methods tailored for the libraries.

Helper Methods vs. Commands

  • Use a helper method if the operation is meant to return a Ruby object that interacts with the application.
    • For example, an admin_user helper method that returns User.where(admin: true).first, which can then be used like login_as(admin_user).
  • Use a command if the operation fits one of the following:
    • A utility operation that performs non-Ruby related tasks, such as IRB's edit command.
    • Displays information, like the show_source command.
    • If the operation requires non-Ruby syntax arguments, like ls -g pattern.

If you don't know what to pick, go with commands first. Commands are generally safer as they can handle a wider variety of inputs and use cases.

Commands

Commands are designed to complete certain tasks or display information for the user, similar to shell commands. Therefore, they are designed to accept a variety of inputs, including those that are not valid Ruby code, such as my_cmd Foo#bar or my_cmd --flag foo.

Example

require "irb/command"

class Greet < IRB::Command::Base
  category "Greeting"
  description "Greets the user"
  help_message <<~HELP
    Greets the user with the given name.

    Usage: greet <name>
  HELP

  # Any input after the command name will be passed as a single string.
  # If nothing is added after the command, an empty string will be passed.
  def execute(arg)
    puts "Hello! #{arg}"
  end
end

IRB::Command.register(:greet, Greet)

As long as the above code is loaded before the IRB session is started, such as in a loaded library or a user's .irbrc file, greet will be accessible to the user.

irb(main):001> greet
Hello!
=> nil
irb(main):002> greet Stan
Hello! Stan
=> nil

And because the Greet command introduces a new category, Greeting, a new help message category will be created:

Help
  help           List all available commands. Use `help <command>` to get information about a specific command.

Greeting
  greet          Greets the user

IRB
  context        Displays current configuration.
  ...

If the optional help_message attribute is specified, help greet will also display it:

irb(main):001> help greet
Greets the user with the given name.

Usage: greet <name>

Helper methods

Helper methods are designed to be used as Ruby methods, such as my_helper(arg, kwarg: val).foo.

The main use case of helper methods is to provide shortcuts for users, providing quick and easy access to frequently used operations or components within the IRB session. For example, a helper method might simplify the process of fetching and displaying specific configuration settings or data structures that would otherwise require multiple steps to access.

Example

# This only loads the minimum components required to define and register a helper method.
# It does not load the entire IRB, nor does it initialize it.
require "irb/helper_method"

class MyHelper < IRB::HelperMethod::Base
  description "This is a test helper"

  def execute(arg, kwarg:)
    "arg: #{arg}, kwarg: #{kwarg}"
  end
end

IRB::HelperMethod.register(:my_helper, MyHelper)

As long as the above code is loaded before the IRB session is started, such as in a loaded library or a user's .irbrc file, my_helper will be accessible to the user.

irb(main):001> my_helper("foo", kwarg: "bar").upcase
=> "ARG: FOO, KWARG: BAR"

The registered helper methods will also be listed in the help message's Helper methods section:

Helper methods
  conf           Returns the current context.
  my_helper      This is a test helper