CODEWITHSUNDEEP
erlangrecord
pandoragami
pandoragami

Reputation: 5585

Erlang: Storing data in a record properly and retrieving it?

I ran the following code with the output 

Erlang R16B (erts-5.10.1) [smp:8:8] [async-threads:10]

Eshell V5.10.1  (abort with ^G)
1> rr(record_io).
[memory]     
2> record_io:store(99).
stored: 2
ok
3> record_io:print().
stored: 2
ok
4>

What I wanted to know is how to do I properly store a value into a record, obviously the output for record_io:print(). should have been 99 and not 2. Heres the code.

-module(record_io).
-export([store/1, print/0]).
-record(memory, {value}).

store(Value) ->
    #memory{ value = Value},
    io:format("stored: ~p~n",[#memory.value]).

print() ->
    io:format("stored: ~p~n",[#memory.value]).

I tried this another way and that too didn't work.

4> c(record_io).
record_io.erl:6: Warning: a term is constructed, but never used
{ok,record_io}
5> rr(record_io).
[memory]
6> record_io:store(S,10).
* 1: variable 'S' is unbound
7>

The code for the modified record_io.

-module(record_io).
    -export([store/2, print/1]).
    -record(memory, {value}).

    store(S,Value) ->
        S#memory{ value = Value},
        io:format("stored: ~p~n",[S#memory.value]),
        S.

    print(S) ->
        io:format("stored: ~p~n",[S#memory.value]).

EDIT: Solution.

The code

-module(record_io).
-export([store/1, print/1]).
-record(memory, {value}).

store(Value) ->
   Rec2 = #memory{ value = Value},
   io:format("stored: ~p~n",[Rec2#memory.value]),
   Rec2.

print(S) ->
   io:format("stored: ~p~n",[S#memory.value]).

The command line.

Rec = record_io:store(99).
record_io:print(Rec).
stored: 99
{memory,99}
stored: 99
ok

Upvotes: 0

Views: 777

Answers (1)

GabiMe
GabiMe

Reputation: 18473

You cannot modify records in Erlang. Only creating new ones. see How do I modify a record in erlang?

Upvotes: 1

Related Questions