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Require libraries without cluttering your namespace.
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README.markdown

Cargo

Require libraries without cluttering your namespace.

Description

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"

How does it work?

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.

Usage

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.

How to prepare your library for Cargo

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.

Installation

$ gem install cargo

License

Copyright (c) 2010 Michel Martens & Damian Janowski

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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