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RedCard provides a standard way to ensure that the running Ruby implementation matches the desired language version, implementation, and implementation version.

NOTE: In this documentation, Ruby version specifies the version of the Ruby programming language itself. Historically, the word "Ruby" could have applied to the language or the original implementation of the language. We refer to the original implementation as MRI or Matz's Ruby Implementation. RedCard distinguishes between Ruby language versions, Ruby implementations, and implementation versions.

Be Liberal

RedCard provides an API for specifying multiple implementations and versions. There are two aspects of this API.

The first one, RedCard.verify, will raise an exception if the requirements are not satisfied.

The parameter, requirements, is an Array of Symbols or Strings with an optional final Hash of implementations as keys and implementation versions as values.

RedCard.verify *requirements

The following examples illustrate RedCard.verify:

# Requires any version JRuby or Rubinius
RedCard.verify :rubinius, :jruby

# Requires Ruby language 1.9 and MRI or Rubinius
RedCard.verify :ruby, :rubinius, "1.9"

# Requires Ruby language 1.9.3 or 2.0
RedCard.verify "1.9.3", "2.0"

# Requires Ruby language 1.9 and Rubinius version 2.0
RedCard.verify "1.9", :rubinius => "2.0"

The second one, RedCard.check will return true if the requirements are satisfied and false if they are not. The requirements parameter has the same specification as for RedCard.verify.

RedCard.check *requirements

The following examples illustrate RedCard.check:

if RedCard.check :rubinius
  # Use Rubinius-specific features

if RedCard.check :ruby, :rubinius, "1.9"
  # Use Ruby language 1.9 features on MRI or Rubinius

if RedCard.check "1.9.3", "2.0"
  # Use Ruby language features found in 1.9.3 or 2.0

if RedCard.check "1.9", :rubinius => "2.0"
  # Use Ruby language 1.9 features on Rubinius version 2.0

Be Conservative

RedCard provides some convenience files that define restrictive requirements. Using these, you can easily restrict the application to a single language version, implementation, and implementation version.

Requiring the file runs RedCard.check with certain parameters matching the specification described by the required files.

The following examples illustrate this:

# Requires at minimum Ruby version 1.9 but accepts anything greater
require 'redcard/1.9'

# Requires Rubinius 2.0
require 'redcard/rubinius/2.0'

# Requires Ruby 1.9 and Rubinius
require 'redcard/1.9'
require 'redcard/rubinius'

Why Do We Need It?

Once upon a time, Ruby was a very simple universe. There was a single Ruby implementation and a single stable version. Now there are multiple current language versions, multiple implementations, and numerous versions of those multiple implementations.

In an ideal world, every Ruby implementation would provide the same features and all such features would have consistent behavior. In the real world, this is not the case. Hence, the need arises to have some facility for restricting the conditions under which an application or library runs. RedCard provides various mechanisms for specifying what language version, implementation, and implementation version are required without resorting to horrific hacks such as if RUBY_VERSION =~ /^1\.8/.