def __init__(self, metadata):
        """
        Initialise an instance.
        :param metadata: The instance of :class:`Metadata` describing this
        distribution.
        """
        self.metadata = metadata
        self.name = metadata.name
        self.key = self.name.lower()    # for case-insensitive comparisons
        self.version = metadata.version
        self.locator = None
        self.digest = None
        self.extras = None      # additional features requested
        self.context = None     # environment marker overrides
        self.download_urls = set()
        self.digests = {}

        Initialise an instance.
        :param metadata: The instance of :class:`Metadata` describing this
        distribution.
        
product/gradle-plugin/src/main/python/pip/_vendor/distlib/database.py