[erlang-questions] Dynamically access record fields

Dmitry Kolesnikov <>
Sat Feb 9 23:57:16 CET 2013


Hello,

> What I was saying was that you can't do something like
> 
> Field = a,
> V2 = setelement(#foo.Field, V1, "A+")


but you can do

Field = #foo.a,
V2 = setelement(Field, V1, "A+")

and do not see any difference, isn't it?

- Dmitry


On Feb 10, 2013, at 12:48 AM, Jeremy Ong <> wrote:

> 
> 
> 
> On Sat, Feb 9, 2013 at 2:33 PM, Dmitry Kolesnikov <> wrote:
> Hello,
> 
> I am not precisely sure what you mean by saying "Erlang doesn't seem to support this …"
> Record is a syntax sugar for tuples, all operations applicable for tuples are also valid for records. 
> Keep in-mind that tuple elements are addressable. 
> 
> 
> -module(rec).
> 
> -export([test/0]).
> 
> -record(foo, {a, b, c}).
> 
> test() ->
>    V1 = #foo{a="A", b="B", c="C"},
>    io:format("rec ~p~n",     [V1]),
>    io:format("rec got ~p~n", [element(#foo.a, V1)]),
>    V2 = setelement(#foo.a, V1, "A+"),
> 
>    io:format("rec ~p~n",     [V2]),
>    io:format("rec got ~p~n", [element(#foo.b, V2)]),
>    V3 = setelement(#foo.b, V2, "B+"),
> 
>    io:format("-> ~p~n",     [V3]).
>  
> 
> 
> What I was saying was that you can't do something like
> 
> Field = a,
> V2 = setelement(#foo.Field, V1, "A+")
>  
> 
> - Dmitry
> 
> 
> On Feb 9, 2013, at 11:40 PM, Jeremy Ong <> wrote:
> 
>> Hmm, upon reading more, it seems like all record functionality is implemented in the compiler pass.
>> 
>> It seems like the ability to address particular variable named locations in tuples would be desirable. I guess I'll have to use proplists or a dict for now, although it feels like overkill for what I'm doing.
>> 
>> 
>> On Sat, Feb 9, 2013 at 1:37 PM, Jeremy Ong <> wrote:
>> Suppose I have a record that looks like
>> 
>> -record(foo, {bucket1, bucket2}).
>> 
>> I may want to pass in an argument specifying what bucket to perform the operation over.
>> 
>> For example,
>> 
>> Bucket = bucket1,
>> 
>> then later,
>> 
>> Use Foo#foo.Bucket for some operations and also modify Bucket with something like
>> 
>> Foo#foo{Bucket = bar}
>> 
>> Erlang doesn't seem to support this, and I don't see why not? Is there a better way to go about this?
>> 
>> Real World Example,
>> 
>> If the record stores data about two people playing a game against one another, and one of them disconnects, I want to perform some operations on the disconnected player's data, and notify the other player that the disconnect occurred. Not having this sort of functionality results in some code duplication and messy code (at least, if using records).
>> 
>> _______________________________________________
>> erlang-questions mailing list
>> 
>> http://erlang.org/mailman/listinfo/erlang-questions
> 
> 

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