[erlang-questions] Best Practice in Map keys: Atoms or Binaries (or Strings)?

Uniaika <>
Sat Oct 1 19:06:38 CEST 2016


There are two things I don't understand in your message:

The first is that Elixir would be backed, or at least similar to
Erlang's records, which isn't quite true, since Elixir's Structs are
built with maps. Maybe you saw something deep in the source code that
made you understand the true nature of structs, but for the moment I'm
keeping the definition provided by the official documentation.

The second thing is the so-called OO nature of Structs. You see them as
objects. If I refer to a definition given by Joe Armstrong (who will
maybe forgive me to bring his article in this context, or maybe not), an
OO object is a cluster of data structures and functions.

So now I'm asking you: How do you manage to access functions from a data
structure that doesn't contain any? I'd be more than happy to be
revealed the great truth beyond the truth concerning structs.

On 10/01/2016 06:39 PM, Vans S wrote:
> That is bad design and advice IMO.  Structs in elixir define object
> orientation, functional programming is about data, everything is data.
>  The tuple being a core building block.
> 
> When you define your application using structures, you have just added
> an extra layer of inference.  Now in most cases that extra layer will
> just get in your way, providing no reasonable benefit.
> 
> One of the biggest enlightenments and problems Erlang developers learn
> early on is the record.  First the record is pretty much a Struct in
> Elixir, with some insignificant differences.  Now most developers would
> do this;  define rigid records like 'User', 'Location', 'Job' with
> default values and  start writing expressions to work with them.  Before
> the developer knows it, the record is being used throughout multiple
> modules across the entire code base. Everything is unit tested and
> static analysis reports the code is 100% excellent, not a single flaw.
> 
> Now the developers code is running in production and its working great! 
> 
> But now a problem comes along, the job the code does has changed,
> storing the email_verification_token inside the 'User' record is no
> longer valid, and a new record is created called 'Validation' that
> houses email_verification_token with sms tokens and other validations.
>  Sure no problem, well defined structure is awesome!
> 
> The entire code base was written rigidly following the spec defined by
> the records (Struct), as soon as we want to make a change now multiple
> modules need to be rewritten.  Now this is not a problem, a day can be
> expent to rewrite/replace 20 modules that use that record. Done,
> rewritten!  
> 
> Now the developers code is running in production and its failing :(
> 
> Turns out by simply replacing text in 20 modules something was missed
> that is producing undefined behavior now. The project is rolled back in
> production to the previous version and the entire development process
> starts all over, trying to figure out where the bug is that was
> introduced from the simple record change.
> 
> 
> Tl; Dr:  Never rely on records (Elixir Structs) across multiple modules,
> always write expressions that manipulate DATA, never write expressions
> that manipulate OBJECTS (oop definition).
> 
> 
> On the count of maps anything used as a key is optimal, there is no
> limitations. Maps are a great flexibility and there is no one right way
> to use them. An example of a useful map key:
> 
> DataChannelLookup#{}
> maps:put({peer1, peer2}, Channel, DataChannelLookup)
> maps:put({peer2, peer1}, Channel, DataChannelLookup)
> maps:put({peer2, peer3}, Channel2, DataChannelLookup)
> maps:put({peer3, peer2}, Channel2, DataChannelLookup)
> 
> Channel2 = maps:get({peer2, peer3}, DataChannelLookup)
> 
> 


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