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diff --git a/trunk/lib/rubygems/requirement.rb b/trunk/lib/rubygems/requirement.rb
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+++ b/trunk/lib/rubygems/requirement.rb
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+#--
+# Copyright 2006 by Chad Fowler, Rich Kilmer, Jim Weirich and others.
+# All rights reserved.
+# See LICENSE.txt for permissions.
+#++
+
+require 'rubygems/version'
+
+##
+# Requirement version includes a prefaced comparator in addition
+# to a version number.
+#
+# A Requirement object can actually contain multiple, er,
+# requirements, as in (> 1.2, < 2.0).
+
+class Gem::Requirement
+
+  include Comparable
+
+  attr_reader :requirements
+
+  OPS = {
+    "="  =>  lambda { |v, r| v == r },
+    "!=" =>  lambda { |v, r| v != r },
+    ">"  =>  lambda { |v, r| v > r },
+    "<"  =>  lambda { |v, r| v < r },
+    ">=" =>  lambda { |v, r| v >= r },
+    "<=" =>  lambda { |v, r| v <= r },
+    "~>" =>  lambda { |v, r| v >= r && v < r.bump }
+  }
+
+  OP_RE = /#{OPS.keys.map{ |k| Regexp.quote k }.join '|'}/o
+
+  ##
+  # Factory method to create a Gem::Requirement object.  Input may be a
+  # Version, a String, or nil.  Intended to simplify client code.
+  #
+  # If the input is "weird", the default version requirement is returned.
+
+  def self.create(input)
+    case input
+    when Gem::Requirement then
+      input
+    when Gem::Version, Array then
+      new input
+    else
+      if input.respond_to? :to_str then
+        self.new [input.to_str]
+      else
+        self.default
+      end
+    end
+  end
+
+  ##
+  # A default "version requirement" can surely _only_ be '>= 0'.
+  #--
+  # This comment once said:
+  #
+  # "A default "version requirement" can surely _only_ be '> 0'."
+
+  def self.default
+    self.new ['>= 0']
+  end
+
+  ##
+  # Constructs a Requirement from +requirements+ which can be a String, a
+  # Gem::Version, or an Array of those.  See parse for details on the
+  # formatting of requirement strings.
+
+  def initialize(requirements)
+    @requirements = case requirements
+                    when Array then
+                      requirements.map do |requirement|
+                        parse(requirement)
+                      end
+                    else
+                      [parse(requirements)]
+                    end
+    @version = nil   # Avoid warnings.
+  end
+
+  ##
+  # Marshal raw requirements, rather than the full object
+
+  def marshal_dump # :nodoc:
+    [@requirements]
+  end
+
+  ##
+  # Load custom marshal format
+
+  def marshal_load(array) # :nodoc:
+    @requirements = array[0]
+    @version = nil
+  end
+
+  def to_s # :nodoc:
+    as_list.join(", ")
+  end
+
+  def as_list
+    normalize
+    @requirements.collect { |req|
+      "#{req[0]} #{req[1]}"
+    }
+  end
+
+  def normalize
+    return if not defined? @version or @version.nil?
+    @requirements = [parse(@version)]
+    @nums = nil
+    @version = nil
+    @op = nil
+  end
+
+  ##
+  # True if this requirement satisfied by the Gem::Version +version+.
+
+  def satisfied_by?(version)
+    normalize
+    @requirements.all? { |op, rv| satisfy?(op, version, rv) }
+  end
+
+  ##
+  # Is "+version+ +op+ +required_version+" satisfied?
+
+  def satisfy?(op, version, required_version)
+    OPS[op].call(version, required_version)
+  end
+
+  ##
+  # Parse the version requirement obj returning the operator and version.
+  #
+  # The requirement can be a String or a Gem::Version.  A String can be an
+  # operator (<, <=, =, =>, >, !=, ~>), a version number, or both, operator
+  # first.
+
+  def parse(obj)
+    case obj
+    when /^\s*(#{OP_RE})\s*([0-9.]+)\s*$/o then
+      [$1, Gem::Version.new($2)]
+    when /^\s*([0-9.]+)\s*$/ then
+      ['=', Gem::Version.new($1)]
+    when /^\s*(#{OP_RE})\s*$/o then
+      [$1, Gem::Version.new('0')]
+    when Gem::Version then
+      ['=', obj]
+    else
+      fail ArgumentError, "Illformed requirement [#{obj.inspect}]"
+    end
+  end
+
+  def <=>(other) # :nodoc:
+    to_s <=> other.to_s
+  end
+
+  def hash # :nodoc:
+    to_s.hash
+  end
+
+end
+