[erlang-questions] Illegal map key in pattern

[Valentin Micic]

Hi,

I am a bit nonplussed with the behaviour of map module…consider the following map:


f(MAP), MAP = #{ {12,1} => "some value", {12,2} => "some other value"}. 


Then, the following works:


f(V), case MAP of #{ {1,12} := V} -> V end.
                            
"some value”



Then, surely, a snippet below should also work... except that it doesn’t: 


 f(DCID), f(SORD), DCID = 12, SORD=1. 

f(V), case MAP of #{ {DCID, SORD} := V} -> V end.

* 1: illegal map key in pattern



To make things worse, when I just replace an explicit term, such as {DCID, SORD}, with something like this:


f(GRP_KEY), GRP_KEY={DCID, SORD}. 

f(V), case MAP of #{ GRP_KEY := V} -> V end.

"some value”



Then the whole thing works again.

I would argue that all cases should just work.
How come they don’t? 


Kind regards

V/

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