def as_dict(self):
return self._copy(_spl_dict)<EOL>
Create a structured schema that will pass stream tuples into callables as ``dict`` instances.
This allows a return to the default calling style for a structured schema.

If this instance represents a common schema then it will be returned
without modification. Stream tuples with common schemas are always passed according
to their definition.

Returns:
    StreamSchema: Schema passing stream tuples as ``dict`` if allowed.

.. versionadded:: 1.8