Discussion: Incorporating Erlang/OTP 21 map guards in Elixir

[Eiji]

@josevalim

In my opinion, the real advantage of map_get/2 and is_map_key/2 is that we can use them to build composable guards. For example, now we can finally implement guards such as is_struct/1 :

I agree with that point.

@josevalim

Discussion #1: Should we add map_get/2 and is_map_key/2 to Kernel?

Normally I would say yes, but keeping previous thing in mind I think that there is no need.

I would say yes if there will be use case for them in real function, so for example I can easily pipe such functions, but in this case I do not see a real need to do that.

@josevalim

Discussion #2: Should we allow patterns in defguard/1 ?

This is awesome idea! It would simplify lots of parts of my code! However I think that it should be separate function like gen_guard (generate guard), because I believe that lots of newbies are confused enough with “normal” guard declarations. Also when adding guards support I (as a definitely non-expert) found few bugs for just only this one feature, so I’m a bit worried whenever guard handling code would be too complicated.

@josevalim

Discussion #3: Should we allow map.field in guards?

Hmm, as you said I think that well used would be awesome feature. I would say that if you believe that your FunctionClauseError messages are well written for all of that weird edge-cases then go for it! Anyway we have forum and community to improve messages if we find that they are confusing.