This is useful when you write a macro that generates a structure with a
known set of fields at macro-expansion time. But sometimes this
known set of fields will be empty.
( Imagine a macro allowing to shortly write some kind of records with
some attributes modified/added/ removed by the macro.
Internally, your macro expand to :
`(let [my_struct (create_struct ~...@keys_generated_by_my_macro)]
in ....
(defn ....)), for example.
if create_struct fails with no keys, then you have to write
(if (empty? keys_generated_by_macro)
(defn ...)
(let [my_struct ...] ....))
Resulting in code duplication: less readable, harder to modify, error
prone.
)
However, (create_struct) seems like a natural generalisation of
(create_struct & keys).
Best,
Nicolas.
On Wed, 2009-06-24 at 10:27 -0500, Mark Volkmann wrote:
> On Wed, Jun 24, 2009 at 10:07 AM, Nicolas Oury
> <[email protected]> wrote:
>
> Dear all,
>
> Sometimes, when I write some macros and applied them to
> special case, I
> got a "create-struct : must supply keys" exception.
>
> I think it should be possible to write (create-struct) and
> have an empty
> structure definition returned.
>
> With (struct (create-struct)) more or less equivalent to
> creating an
> empty map.
>
> Currently, it results in some special case in macros or adding
> a :dummy
> field to any generated struct.
>
> If you don't know the keys in advance then why not create a map
> instead? For me the point of using a struct is that you get optimized
> access to a known set of keys and the struct documents the keys you
> expect to use. You can't get those benefits without knowing the keys.
>
> --
> R. Mark Volkmann
> Object Computing, Inc.
>
> >
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