# File lib/rubygems/installer.rb, line 59
  def initialize(gem, options={})
    @gem = gem

    options = {
      :force => false,
      :install_dir => Gem.dir,
      :exec_format => false,
    }.merge options

    @env_shebang = options[:env_shebang]
    @force = options[:force]
    gem_home = options[:install_dir]
    @gem_home = Pathname.new(gem_home).expand_path
    @ignore_dependencies = options[:ignore_dependencies]
    @format_executable = options[:format_executable]
    @security_policy = options[:security_policy]
    @wrappers = options[:wrappers]
    @skip_dependencies = options[:skip_dependencies]

    begin
      @format = Gem::Format.from_file_by_path @gem, @security_policy
    rescue Gem::Package::FormatError
      raise Gem::InstallError, "invalid gem format for #{@gem}"
    end

    @spec = @format.spec

    @gem_dir = File.join(@gem_home, "gems", @spec.full_name).untaint
  end