[erlang-questions] Unexpected list_to_binary behavior

Valentin Micic <>
Tue Mar 18 15:15:57 CET 2014


Yes, you're right and this make sense at some level, particularly if the function I've called was

characters_to_binary/1.

Indeed, as Magnus Henoch mentioned in a related email, there is a function for conversion of unicode characters:

unicode:characters_to_binary/1;

So, why should the other one be called: list_to_binary/1 instead instead of characters_to_binary/1

If one disregard the existence of any previous knowledge, and given that a list may contain any number of arbitrary types, including a list itself,  what should be a reasonable expectation for (and here's the kicker -- not an input argument itself, for it is perfectly acceptable to assume it to be a list, but) a content of the input argument?

It's surprising (at least was to me) to expect a content of an input argument ( formerly known as list ) to be limited to a list of octets, as much as it is surprising to see that  integer_to_binary( 65536 ) results in <<"65536">> instead of <<255,255>>, that is, surprising to se that it behaves like a shortcut to  list_to_binary( integer_to_list( 65536 )).

On the other hand, it is what it is, and, in a way,  I am quite embarrassed that I assumed that integers would be automagically converted to appropriate number of octets, for this is just as unreasonable and arbitrary expectation. 

Thank you for your responses.

Kind regards

V/


On 18 Mar 2014, at 3:19 PM, Steve Vinoski wrote:

> 
> 
> 
> On Tue, Mar 18, 2014 at 9:13 AM, Valentin Micic <> wrote:
> Hi all,
> 
> (my apologies if this has been covered already)
> 
> Is there any reason why:
> 
> ()820> list_to_binary( lists:seq(1,255) ).
> <<1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,
>   22,23,24,25,26,27,28,29,…>>
> 
> works, but 
> 
> ()821> list_to_binary( lists:seq(1,256) ).
> ** exception error: bad argument
>      in function  list_to_binary/1
>         called as list_to_binary([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,
>                                   23,24,25,26,27,28|…])
> 
> breaks on Erlang 16B02? Was the limit to 255 characters for list_to_binary/1 always there and I just failed to see it before?
> 
> This has nothing to do with the number of characters, but rather that you can't represent the value 256 in a byte:
> 
> 1> list_to_binary([256]).
> ** exception error: bad argument
>      in function  list_to_binary/1
>         called as list_to_binary([256])
> 
> --steve

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