[erlang-questions] Record typing for dialyzer

[Paul Mineiro]

I had the same problem.

I ended up keeping the type signature in the declaration strict, and using
setelement/3 to construct the type-violating version of the record that I
pass to mnesia:select/2.

-- p

On Wed, 25 Nov 2009, Bernard Duggan wrote:

> Hi list,
>     We have a lot of auto-generated record types that we use to allow
> our (newer, awesomer) erlang/mnesia code to interact with our (older,
> less awesome, but we're stuck with it for now) C++/mysql code.  It
> recently occurred to me that it would be a simple matter to add type
> specifiers to the records to give dialyzer (which we love to death) some
> extra info to work with.  And for the most part it was.  So we now have
> nice auto-generated records of the form:
>
> -record( person{
>     id :: integer(),
>     name :: string(),
>     is_awesome :: boolean()
> }).
>
> which is great (and already helped us find several bugs - have I
> mentioned we love dialyzer?).  We struck a problem, however, when we
> used one of our records in a select statement thus:
>
> Match = #person{name="Bernie", id='$1', _='_'},
> mnesia:select(person, [{Match, [], [{{'$1'}}]}]),
>
> At this point, dialyzer quite correctly points out that '$1' isn't an
> integer and '_' isn't a boolean and so we've got no business assigning
> them to fields typed as such.
>
> My solution, then was to add an extra type definition:
>
> -type search_spec() :: '_' | '$1' | '$2' | '$3' | '$4' | '$5' | '$6' |
> '$7' | '$8' | '$9'.
>
> and change all the record definitions to something like:
>
> -record( person{
>     id :: integer() | search_spec(),
>     name :: string() | search_spec(),
>     is_awesome :: boolean() | search_spec()
> }).
>
> Now this solves the problem, but it really looks ugly and seems like
> kind of a hack and I can't help but feel like there must be some more
> elegant solution.  But I don't know what it is :)  Any input (even if
> it's only "nope, there's no better way to do it") would be greatly
> appreciated.
>
> Cheers,
>
> Bernard
>
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