Indeed, this is a confusing trap for beginners, especially if you come from languages where order of the functions don’t matter, thank God for compiler warnings.
D4no0
dimitarvp
You can read about it here, it’s IMO well-explained: Elixir, A Little Beyond The Basics - Part 8: genservers
One very important excerpt about the process messages:
# send
:hello
# cast
{:"$gen_cast", :hello}
# call
{ :"$gen_call",
{#PID<0.110.0>, [:alias | #Reference<0.426212949.4092919813.244647>]},
:hello
}
GenServer.cast and GenServer.call basically do send messages with an opinionated format. There’s no magic, just stuff that’s handled for you so you have an easier time – that’s all really.
But if you want to start peeking under the hood you have to make sure you either don’t match on these special messages or you do get them but also forward them further, otherwise GenServer.cast and GenServer.call will not work.
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