Re: [PATCH] adjust warning_n() to take uhwi (PR 84207)

[Pedro Alves <palves at redhat dot com>]

On 02/14/2018 09:47 PM, Manuel López-Ibáñez wrote:
> On 14 Feb 2018 8:16 pm, "Pedro Alves" <palves@redhat.com <mailto:palves@redhat.com>> wrote:
> 
>     Instead of a class that has to have a constructor for every type
>     you want to pass as plural selector to the _n functions, which
>     increases coupling, I'd suggest using a conversion function, and
>     overload that.  I.e., something like, in the core diagnostics code:
> 
>     static inline unsigned HOST_WIDE_INT
>     as_plural_form (unsigned HOST_WIDE_INT val)
>     {
>       return val;
>     }
> 
>     /* In some tree-diagnostics header.  */
> 
>     static inline unsigned HOST_WIDE_INT
>     as_plural_form (tree t)
>     {
>        // extract & return a HWI
>     }
> 
>     /* In some whatever-other-type-diagnostics header.  */
> 
>     static inline unsigned HOST_WIDE_INT
>     as_plural_form (whatever_other_type v)
>     {
>        // like above
>     }
> 
>     and then you call error_n and other similar functions like this:
> 
>         error_n (loc, u, "%u thing", "%u things", u);
>         error_n (loc, as_plural_form (u), "%u thing", "%u things", u);
>         error_n (loc, as_plural_form (t), "%E thing", "%E things", t);
>         error_n (loc, as_plural_form (i), "%wu thing", "%wu things", i);
> 
>     This is similar in spirit to std::to_string, etc.
> 
> 
> If that's desired, why not simply have GCC::to_uhwi() ? It would likely be useful in other contexts.

Because of types that (e.g. wide_int specializations) that can store
values larger than what fit in uhwi.  GCC::to_uhwi's semantics for that
aren't clear -- could saturate, could unsigned wrap, could
throw/abort/assert, could be undefined.

as_plural_form has clear semantics -- it'd return a value that does
the right thing for ngettext's N parameter.  I.e., it'd do
the "n % 1000000 + 1000000" operation as a wide_int still, and
before converting/cast the result to uhwi. 

Thanks,
Pedro Alves