Options for "soft" script dependencies

askrubygems.rb

if Gem::Specification.find_all_by_name("clipboard", "~> 1.0").any?
  gem "clipboard", "~> 1.0"
  require "clipboard"
  # ...
end

rescue.rb

begin
  gem "clipboard", "~> 1.0"
  require "clipboard"
  # ...
rescue LoadError
  # NOOP
end

Note that both versions lock the version down to the 1.* range. I have a sense that the rescue.rb version, which I see most often, is largely cargo-culted from the pre-RubyGems era. But on the other hand, I might be missing something.

I'd really hate to tell people to type all of line 1 of askrubygems.rb, but that's my only objection to it.

rescue.rb's flaw is line 5 and 6 that you have to add as boilerplate and can get wrong due to LoadError / Gem::LoadError typos or confusion (see PS below).

It seems like RubyGems should add a method that:

• Returns a true-value if a gem with a version is installed (maybe specification?)
• Returns false if a gem with a version is not installed
• Activates the given version if it is installed

This would allow for the minimum typing:

if Gem.NAME_HERE 'clipboard', '~> 1.0
  require 'clipboard
  # …
end

PS: Line 5 of rescue.rb should be rescue Gem::LoadError.

You shouldn't need to rescue LoadError (as I'm sure you realize) as matching the gem name to the require name is a best practice already.

In this instance the cargo cult built a functional airport.

You may be thinking of:

begin
  require 'rubygems'

  gem 'some_gem'
rescue LoadError, Gem::LoadError
end

require 'some_gem'

Which would allow you to load some_gem regardless of how it was installed.