Hi, As I mentioned in an earlier topic, I’m playing with building an elixir client for the AWS apis from api definitions they provide. These apis have lots of different return types, also described by these api definitions. I’m wondering what data types the elixir implementations should return. Th…

[image] fcheung: Is it because each struct is module and there is a cost to pay for each module? Yes. [image] fcheung: Is this this something to worry about normally or is only edge cases with hundreds of modules per file that are affected? Only when defining hundreds.

As a long time erlang user I like Records, but maps/structs have supplanted their use. Just note, a record is just a tuple with some compile-time names given. I’d have to know more about your use-case and why maps are slow for you, and given that I’m not sure records would be much faster. Can you…

AWS API responses are XML E.g. <DescribeKeyPairsResponse xmlns="http://ec2.amazonaws.com/doc/2015-10-01/"> <requestId>7a62c49f-347e-4fc4-9331-6e8eEXAMPLE</requestId> <keySet> <item> <keyName>gsg-keypair</keyName> <keyFingerprint> 00:00:00:00:00:00:00:00:00:00:00:00:00:…

The number of structures is dictated by the number of data types that the api description files define - 276 for the rds api , 536 for the ec2 one, 225 for IAM etc. Across 72 apis / api versions that adds up to a lot of structs. I’m not sure about runtime slowness - I haven’t written enough of this…

[image] fcheung: The number of structures is dictated by the number of data types that the api description files define - 276 for the rds api , 536 for the ec2 one, 225 for IAM etc. Across 72 apis / api versions that adds up to a lot of structs. The sheer amount of data types seems to make th…

That makes sense. I can populate the maps with nils for fields that are optional in api responses.

One other thing, aside from what is the correct interface, why is it that defining lots of structs causing slow compile times? Is it because each struct is module and there is a cost to pay for each module? Is this this something to worry about normally or is only edge cases with hundreds of module…

It looks like Postgrex makes heavy use of records for a similar use case. Is there a distinction that I’m missing? Or would you recommend this be built differently if done today?

Maps are a fairly recent development in the BEAM world, most uses of Records are better served by Structs nowadays, and Postgrex has been around a long while. :slight_smile: Records are still technically better in some ways, like accessing a field in it is ‘slightly’ faster than a map, but inserti…

Think of records as glorified tuples. When you need to handle multiple different tuples, which are private to a module, records work great. Maps would also work in the example above, but they wouldn’t give the compile time guarantee of records. Structs would be too wasteful though for those cases. T…

Thanks, @josevalim . That’s helpful!

Choosing between maps, structs, records etc

Questions & Help Questions

josevalim September 28, 2016, 1:12pm 8

Yes.

Only when defining hundreds.