I am attempting to create a function that stores a number into a record and then adds value X to that number every time the function runs.
Value: 5
Run Function (Add One): 1
Value should be: 6
Run Function (Add One): 1
value should be 7
I tried to use a record:
-record(adder,{value :: integer()}).
---function
Number = random:uniform(6),
L=#added{value = Number + #added.value}.
This does not work as it resets the value every time. Any suggestions?
Take a look at this code:
-module(test).
-export([add/1]).
-record(adder, {value=6}).
add(X) ->
#adder{value = X + #adder.value}.
If you compile this in your shell, any call to "add(3)" will result in "{adder,5}" and not in "{adder, 9}". Take a look:
Eshell V6.4 (abort with ^G)
1> c(test).
{ok,test}
2> test:add(3).
{adder,5}
3> test:add(3).
{adder,5}
How come? This is because records are actually tuples. The expression "#adder.value" in the last line is evaluated as the position of the field "value" in your adder tuple, which is 2. Let's have some proof. Change the definition of your record:
-module(test).
-export([add/1]).
-record(adder, {field1, field2, value=6}).
add(X) ->
#adder{value = X + #adder.value}.
Now, recompiling your code and calling add(3) again would result in
1> c(test).
{ok,test}
2> test:add(3).
{adder,undefined,undefined,7}
I've asked myself, how you came up with this question. Didn't you want your function to be something like this?
add2(#adder{value = V} = R, X) ->
R#adder{value = V + X}.