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Add compare parameter to MapStream. #38

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Merged
cmeyer merged 1 commit into from
Oct 8, 2025
Merged

Add compare parameter to MapStream. #38

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5 changes: 3 additions & 2 deletions nion/utils/Stream.py
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Original file line number Diff line number Diff line change
Expand Up @@ -125,19 +125,20 @@ def _send_value(self) -> None:
class MapStream(AbstractStream[OT], typing.Generic[T, OT]):
"""A stream that applies a function when input streams change."""

def __init__(self, stream: AbstractStream[T], value_fn: typing.Callable[[typing.Optional[T]], typing.Optional[OT]]) -> None:
def __init__(self, stream: AbstractStream[T], value_fn: typing.Callable[[typing.Optional[T]], typing.Optional[OT]], cmp: typing.Optional[EqualityOperator] = None) -> None:
super().__init__()
# outgoing messages
self.value_stream = Event.Event()
# references
self.__stream = stream
cmp = cmp if cmp else operator.eq
# initialize values
self.__value: typing.Optional[OT] = None

# listen for display changes
def update_value(stream: MapStream[T, OT], value: typing.Optional[T]) -> None:
new_value = value_fn(value)
if new_value != stream.value:
if not cmp(new_value, stream.value):
stream.send_value(new_value)

# use weak_partial to avoid holding references to self.
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