[erlang-questions] -spec tuple variable size

Dmitry Kolesnikov <>
Thu Nov 29 17:46:28 CET 2012


Hello,

Thanks for your comment, appreciate it.
Unfortunately, you have missed my use-case.

I do offer an api to store a tuple. The storage do not concern the tuple cardinality, in similar fashion like ets/dets does. One of my current limitation is that tuple elements MUST be a particular data type. I simply want to validate that client writes tuples with supported data types. I am also fine with generic tuple() data type but it is less error prone.

- Dmitry

On Nov 29, 2012, at 6:24 PM, Siraaj Khandkar <> wrote:

> 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 <> 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 <> 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 <> 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 <> wrote:
>>>> 
>>>>> On Wed, Nov 28, 2012 at 9:10 PM, Dmitry Kolesnikov
>>>>> <> 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
> .o.
> ..o
> ooo
> 




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