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Fiddle

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A libffi wrapper for Ruby.

Fiddle is an extension to translate a foreign function interface (FFI) with ruby.

It wraps libffi, a popular C library which provides a portable interface that allows code written in one language to call code written in another language.

Installation

Add this line to your application's Gemfile:

gem 'fiddle'

And then execute:

$ bundle

Or install it yourself as:

$ gem install fiddle

Usage

Here we will use Fiddle::Function to wrap floor(3) from libm

require 'fiddle'

libm = Fiddle.dlopen('/lib/libm.so.6')

floor = Fiddle::Function.new(
          libm['floor'],
          [Fiddle::TYPE_DOUBLE],
          Fiddle::TYPE_DOUBLE
        )

puts floor.call(3.14159) #=> 3.0

Nested Structs

You can use hashes to create nested structs, where the hash keys are member names and the values are the nested structs:

StudentCollegeDetail = struct [
  'int college_id',
  'char college_name[50]'
]

StudentDetail = struct [
  'int id',
  'char name[20]',
  { clg_data: StudentCollegeDetail }
]

You can also specify an anonymous nested struct, like so:

StudentDetail = struct [
  'int id',
  'char name[20]',
  {
    clg_data: struct([
                      'int college_id',
                      'char college_name[50]'
                    ])
  }
]

The position of a hash (and the order of the keys in the hash, in the case of a hash with multiple entries), dictate the offsets of the nested struct in memory. The following examples are both syntactically valid but will lay out the structs differently in memory:

# order of members in memory: position, id, dimensions
Rect = struct [ { position: struct(['float x', 'float y']) },
                'int id',
                { dimensions: struct(['float w', 'float h']) }
              ]

# order of members in memory: id, position, dimensions
Rect = struct [ 'int id',
                {
                  position: struct(['float x', 'float y']),
                  dimensions: struct(['float w', 'float h'])
                }
              ]

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ruby/fiddle.

License

The gem is available as open source under the terms of the BSD-2-Clause.

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