Cstubs.Types.TYPE.const consumption

[dsheets]

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What functions can consume Cstubs.Types.TYPE.const and return something useful?

Only Cstubs.Types.TYPE.enum as far as I can tell.

What if you have constants that were not in an enum? For instance, a group of macros does not appear to have a way to be mapped into variant constructors. Have a missed something?

[yallop]

What if you have constants that were not in an enum? For instance, a group of macros does not appear to have a way to be mapped into variant constructors. Have a missed something?

I think for the moment you have to process the results of the macros outside the functor:

module Type_bindings(T: Cstubs.Types.TYPE) = struct
   let macro_a = constant "MACRO_A" int64
   and macro_b = constant "MACRO_B" int64
   and macro_c = constant "MACRO_C" int64
end

[...]
(* in some other file *)
module Bindings = Type_bindings(Generated_type_stubs)

(* Bindings.macro_{a|b|c} are now int64 values, which you can map to
   variant contructors etc. *)

More generally, const is currently pretty limited and could perhaps be relocated to the more general Ctypes_types.TYPE signature, since there are quite a few other situations where it could be used to retrieve and use compile-time information:

• The array constructor could have the type

  val array : int const -> 'a typ -> 'a carray typ
  

  so that we could construct arrays with lengths that are known at compile-time:

  #define TABLE_ENTRIES 10
  
  struct table {
    int id;
    struct entry *entries[TABLE_ENTRIES];
  };
  

• Similarly, the abstract constructor could take its size and alignment arguments as const values.

• The sizeof and alignment functions could return int const so that they could be computed in generated C code and used to construct other static elements

We could also make const an applicative, which should make it possible to move various computations back inside the bindings functor.

[dsheets]

I need a constant_opt (or macro_opt?) function for macros that may not be defined which would introduce an #ifdef and return None if the macro is missing.