Add quick Registry example to GenServer docs #14368
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nathanl
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| Registry.lookup(:stacks, "stack 1") | ||
| #=> [{#PID<0.150.0>, nil}] |
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@nathanl Registry.lookup/2 is a dangerous pitfall (ask me how I know...) because it won't work if you attach metadata to the :via tuple. Maybe we use GenServer.whereis/1 in this example?
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@whatyouhide I'm trying to add an example of the advice in the previous paragraph regarding Registry. GenServer.whereis/1 is for global atom names only, right?
I wasn't aware that Registry could store metadata, but it looks like Registry.lookup/2 can fetch it.
metadata = "taters"
{:ok, _} = Registry.register(:stacks, 9, metadata)
Registry.lookup(:stacks, 9)
[{#PID<0.138.0>, "taters"}] # value == "metadata"?
Registry.lookup(:stacks, :bob) # registered with a :via tuple
[{#PID<0.137.0>, nil}]I see in the v1.19.0-dev docs that {:via will be able to include metadata soon - is that when lookup/2 becomes a problem? What am I missing?
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Yes that's when lookup/2 becomes a problem. I would just register via :via here but use GenServer.whereis instead of Registry.lookup.
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