Re: [PATCH 4/6] Constify some parameters in the varobj code

[Pedro Alves <palves@redhat.com>]

On 01/29/2015 08:28 PM, Simon Marchi wrote:
> To make it clear that some functions should not modify the variable
> object, this patch adds the const qualifier where it makes sense to some
> struct varobj * parameters. Most getters should take a const pointer to
> guarantee they don't modify the object.
> 
> Unfortunately, I couldn't add it to some callbacks (such as name_of_child).
> In the C implementation, they call c_describe_child, which calls
> varobj_get_path_expr. varobj_get_path_expr needs to modify the object in
> order to cache the computed value. It therefore can't take a const
> pointer, and it affects the whole call chain. I suppose that's where you
> would use a "mutable" in C++.

FYI, in these cases it's totally fine to have the function take a const pointer,
and then cast away the const inside the function.  We do exactly that in
a few places.  E.g.:

/* Returns the decoded name of GSYMBOL, as for ada_decode, caching it
   in the language-specific part of GSYMBOL, if it has not been
   previously computed.  Tries to save the decoded name in the same
   obstack as GSYMBOL, if possible, and otherwise on the heap (so that,
   in any case, the decoded symbol has a lifetime at least that of
   GSYMBOL).
   The GSYMBOL parameter is "mutable" in the C++ sense: logically
   const, but nevertheless modified to a semantically equivalent form
   when a decoded name is cached in it.  */

const char *
ada_decode_symbol (const struct general_symbol_info *arg)
{
  struct general_symbol_info *gsymbol = (struct general_symbol_info *) arg;
...

Thanks,
Pedro Alves