On Wed, 2014-08-13 at 12:07 +0200, Richard Biener wrote: > On Wed, Aug 13, 2014 at 12:01 PM, Martin Jambor <mjam...@suse.cz> wrote: > > Hi, > > > > On Wed, Aug 06, 2014 at 01:19:44PM -0400, David Malcolm wrote: > >> In many circumstances, is_a_helper <T>::test assumes that the pointer is > >> non-NULL, but sometimes you have a pointer of type T that can be NULL. > >> > >> Earlier versions of this patch kit made numerous uses of the ternary > >> operator to handle nullable pointers e.g.: > >> > >> return insn ? as_a <rtx_insn *> (insn) : NULL; > >> > >> but this was ugly. Instead, introduce an as_a_nullable<T> variant that > >> adds a check for NULL, so the above can be written simply as: > >> > >> return as_a_nullable <rtx_insn *> (insn); > > > > A tiny bikeshedding, disregard it if you don't like it: however, the > > "nullable" part of the name suggests the pointer can be NULLed in the > > process. I think that variants of functions that survive NULL > > arguments are traditionally called "safe" in gcc, so what about > > "safe_as" (or safely_as)? > > Ok, I resisted at first starting the bike-shedding but I agree on > the badness of "nullable" (what does that mean anyway?). > as_a_safe or safe_as_a both work for me.
I think I took the terminology from: http://en.wikipedia.org/wiki/Nullable_type meaning "something that can be NULL". "safe" as a prefix seems to be the pattern in the rest of the code, so I guess I'll use "safe_as_a". Thanks Dave > Richard. > > > > > Martin > > > > > >> > >> gcc/ > >> * is-a.h (template<T, U> as_a_nullable <U *p>) New function. > >> --- > >> gcc/is-a.h | 24 ++++++++++++++++++++++++ > >> 1 file changed, 24 insertions(+) > >> > >> diff --git a/gcc/is-a.h b/gcc/is-a.h > >> index a14e344..f50e62c 100644 > >> --- a/gcc/is-a.h > >> +++ b/gcc/is-a.h > >> @@ -46,6 +46,14 @@ TYPE as_a <TYPE> (pointer) > >> > >> do_something_with (as_a <cgraph_node *> *ptr); > >> > >> +TYPE as_a_nullable <TYPE> (pointer) > >> + > >> + Like as_a <TYPE> (pointer), but where pointer could be NULL. This > >> + adds a check against NULL where the regular is_a_helper hook for TYPE > >> + assumes non-NULL. > >> + > >> + do_something_with (as_a_nullable <cgraph_node *> *ptr); > >> + > >> TYPE dyn_cast <TYPE> (pointer) > >> > >> Converts pointer to TYPE if and only if "is_a <TYPE> pointer". > >> Otherwise, > >> @@ -185,6 +193,22 @@ as_a (U *p) > >> return is_a_helper <T>::cast (p); > >> } > >> > >> +/* Similar to as_a<>, but where the pointer can be NULL, even if > >> + is_a_helper<T> doesn't check for NULL. */ > >> + > >> +template <typename T, typename U> > >> +inline T > >> +as_a_nullable (U *p) > >> +{ > >> + if (p) > >> + { > >> + gcc_checking_assert (is_a <T> (p)); > >> + return is_a_helper <T>::cast (p); > >> + } > >> + else > >> + return NULL; > >> +} > >> + > >> /* A generic checked conversion from a base type U to a derived type T. > >> See > >> the discussion above for when to use this function. */ > >> > >> -- > >> 1.8.5.3 > >>
