Cargo

Require libraries without cluttering your namespace.

Consider these two versions of the same library:

# foo-1.0.0.rb
class Foo
  VERSION = "1.0.0"
end

# foo-2.0.0.rb
class Foo
  VERSION = "2.0.0"
end

If you want to use both of them in your application, require and load will be of little help. Consider what happens when you require both libraries:

>> require "foo-1.0.0"
=> true
>> require "foo-2.0.0"
=> true
>> Foo::VERSION
=> "2.0.0"

As both files are opening the same class, there's no way for you to use them independently.

Cargo solves that problem in a very simple way:

>> Foo1 = import("foo-1.0.0")
=> #<Module:0x000001009ffa28>::Foo
>> Foo2 = import("foo-2.0.0")
=> #<Module:0x000001009f2828>::Foo
>> Foo1::VERSION
=> "1.0.0"
>> Foo2::VERSION
=> "2.0.0"

The command Kernel.load accepts a second parameter, which value is false by default. When the passed value is true, the script is executed under an anonymous module, protecting the calling program's global namespace. No local variables in the loaded file are propagated to the loading environment.

By using a global module as a temporal storage, it is possible to transfer a value from the anonymous module to the caller program.

After requiring cargo in the calling program, two methods will be available: import and export. Both use the global module Cargo for temporal storage.

This is how you will use it in the calling program:

$ cat calling_program.rb
require "cargo"

MyFoo = import("foo")

And for that to work, the imported library should look like this:

$ cat foo.rb
class Foo
  VERSION = "1.0.0"
end

export(Foo)

Note that you can only export one value per file. Multiple calls to export just change the value to be exported. This constraint is in place in order to make for a simple and clean implementation.

In your library entry point, you need to use export and provide a value. As the export method won't be available unless the caller is using Cargo, you can make a conditional call:

export(Foo) if defined?(export)

If your library has just one file, that single line will make your code ready to be imported. Otherwise, you will need to require Cargo and make sure you don't mix import with require for local files.

$ gem install cargo

Copyright (c) 2010 Michel Martens & Damian Janowski

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