[erlang-questions] -spec tuple variable size

Siraaj Khandkar siraaj@REDACTED
Thu Nov 29 17:24:03 CET 2012

Hmmm, IDK, that just seems wrong to me. If what you're offering clients is a
variable number of elements, then, semantically, you're offering them a list.
If a client wants to optimize lookups, it should be left up to the client app
to convert it to a tuple.

If you think about it, you're asking for a static guarantee for something that
is only known at runtime, which is not possible.

Alternatively, I guess you can write a template that expands to 4096 elements :)

On Nov 29, 2012, at 11:08 AM, Dmitry Kolesnikov <dmkolesnikov@REDACTED> wrote:

> Hello,
> Yes, you are right that tuples are converted into list during the serialisation process. You cannot avoid it but api offered to client uses tuples. 
> - Dmitry
> On Nov 29, 2012, at 6:03 PM, Siraaj Khandkar <siraaj@REDACTED> wrote:
>> I don't know all the technicalities of Erlang's type specs, but in general -
>> variable growth is antithetical to the concept of a tuple.
>> You'll still need to accumulate the elements in some list before you convert
>> it to a tuple, so why not just spec that list?
>> On Nov 28, 2012, at 5:10 PM, Dmitry Kolesnikov <dmkolesnikov@REDACTED> wrote:
>>> Hello,
>>> Thanks for response!
>>> Let me explain better what I am trying to achieve.
>>> "The shorthand [T,...] stands for the set of non-empty proper lists whose elements are of type T." 
>>> I am looking for similar definition but for tuples.
>>> My application serialises tuples into disk. The size of tuple is unbound but tuple elements a fixed to string, binary, number, boolean or undefined. I cannot use " "|" operator to define as many variants as you like" because number of variants is unlimited. Well practically, I do have a hard limit of 4096 elements per tuple but I am lazy to type in 4096 variants :-) 
>>> - Dmitry
>>> On Nov 28, 2012, at 11:50 PM, Motiejus Jakštys <desired.mta@REDACTED> wrote:
>>>> On Wed, Nov 28, 2012 at 9:10 PM, Dmitry Kolesnikov
>>>> <dmkolesnikov@REDACTED> wrote:
>>>>> but compiler fails syntax error before: ','
>>>>> -- CLIP --
>>>>> -type value()     :: string() | binary() | number() | boolean() | undefined.
>>>>> -type entity()    :: [{atom(), value()}] | {field()}.
>>>> These should be fine.
>>>>> -type field()      :: value() | value(), field().
>>>> Maybe you meant
>>>> -type field() :: value() | {value(), field()}.
>>>> ?
>>>> In general, if you want to define tuples of different sizes in -spec,
>>>> you use the "|" operator to define as many variants as you like.
>>>> Likely I don't understand what you are trying to define.

Siraaj Khandkar

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