Record typing for dialyzer

Bernard Duggan bernie@REDACTED
Wed Nov 25 00:37:28 CET 2009

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



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