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Extensible dispatchers #97
Description
I'm working on a library that will provide some default dispatchers, using the @dispatcher.register(type) syntax.
In [8]: default_dispatcher = multipledispatch.Dispatcher("default")
In [9]: import json
In [10]: @default_dispatcher.register(dict)
...: def _(obj):
...: return json.dumps(obj)
...: I'd like users to be able to extend my dispatcher into their own.
In [11]: user_dispatcher = multipledispatch.Dispatcher('user')
In [12]: user_dispatcher.funcs = default_dispatcher.funcs.copy()
In [13]: @user_dispatcher.register(list)
...: def _(obj):
...: return json.dumps(list)
...: Syntactically, this is a bit awkward. I know there's the @dispatch(namespace=d) API, but this requires the user to remember to add the namespace argument on every decoration, which seems potentially more error-prone than d.register().
How would you feel about providing some extensibility options? For example, using a ChainMap or dict it might be
# multipledispatch code
class ExtensibleDispatcher:
def __init__(self, funcs=None, doc=None):
self.funcs = collections.ChainMap(funcs)
self.doc = doc
def evolve(self, registry=None):
return type(self)(self.funcs.new_child(registry or {}), self.doc)
# client library code
d = ExtensibleDispatcher()
@d.register(dict)
def _(obj):
return json.dumps(obj)
# user code
d2 = d.evolve()
@d2.register(list)
def _(obj):
return json.dumps(obj)But it could even be as simple as adding a funcs argument to the Dispatcher constructor to allow
user_dispatcher = Dispatcher(name='new', funcs=default_dispatcher.copy())
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