MEMBER_TYPE and CV qualifiers

[Mark Mitchell]

Giovanni Bajo wrote:
> Mark Mitchell <mark@codesourcery.com> wrote:
> 
> 
>>The function type is no more
>>cv-qualified than any other function type; the only thing that's
>>cv-qualified is the type pointed to by the first argument.
> 
> 
> The standard does not agree with you though, see 9.3.1/3.

It does indeed say that.

I've already said that it might make sense to put the cv-qualifiers in 
both places, but I've also said that I think it's dangerous, because you 
have to keep the two places in synch, and that's always been risky.  You 
also have to deal with the fact that much of the compiler may assume 
function types are not cv-qualified.  Furthermore, you have to be 
careful of things like the fact that you cannot assign a 
pointer-to-nonconst-member-function to a 
pointer-to-const-member-function, even though, of course, you can assign 
a "T*" to a "const T*" if "T" is an object type.  So, there are still 
special cases.

Furthermore, 9.3.1/3 is at odds with 3.9.3/1, which says:

   Each type which is  a  cv-unqualified  complete  or
   incomplete  object  type  or  is void (_basic.types_) has three corre-
   sponding cv-qualified versions of its type: a const-qualified version,
   a  volatile-qualified version, and a const-volatile-qualified version.

Note that it explicitly leaves out function types.

Obviously, the most important thing is to get the right behavior. 
Following the standard in our internal representation is secondary -- 
but highly desirable.  In this case, my opinion is that it's a bad idea 
to put the cv-qualifiers on the FUNCTION_TYPE; I'd rather see the 
special cases.  And, maybe, cp_type_quals should be taught about this 
case -- we're already supposed to be using that in most places.

-- 
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com
(916) 791-8304