| Message ID | 51D6DB8A.7030507@oracle.com |
|---|---|
| State | New |
| Headers | show |
Paolo Carlini <paolo.carlini@oracle.com> writes: | Hi, | | this issue dates back to 2004 and got stalled pretty soon. Essentially | Gaby wanted to see *dynamic_cast* explicitly mentioned in this kind of | diagnostic (we used to explicitly talk about static_cast), whereas | Mark found the current status an improvement over the past, proposed | some further, minor, improvements (which I tried to implement in the | below) | | Today I noticed that current ICC, clang, OracleStudio, all produce | diagnostic quite similar, modulo the latter improvements, to GCC and | decided to explore whether Gaby (and Jason) would like to reassess the | bug, whether today we want to talk about dynamic_cast. | | Tested x86_64-linux. | | Thanks, | Paolo. I still consider talk of 'static_cast' in this context a non-starter. However, maybe just saying "convert" would be OK -- though clearly giving hints of dynamic_cast is much better. Minor nits: say "base class" instead of "base", and "derived class" instead of "derived type". Otherwise, patch OK with these suggestions. -- Gaby
Hi, On 07/05/2013 05:36 PM, Gabriel Dos Reis wrote: > Paolo Carlini <paolo.carlini@oracle.com> writes: > > | Hi, > | > | this issue dates back to 2004 and got stalled pretty soon. Essentially > | Gaby wanted to see *dynamic_cast* explicitly mentioned in this kind of > | diagnostic (we used to explicitly talk about static_cast), whereas > | Mark found the current status an improvement over the past, proposed > | some further, minor, improvements (which I tried to implement in the > | below) > | > | Today I noticed that current ICC, clang, OracleStudio, all produce > | diagnostic quite similar, modulo the latter improvements, to GCC and > | decided to explore whether Gaby (and Jason) would like to reassess the > | bug, whether today we want to talk about dynamic_cast. > | > | Tested x86_64-linux. > | > | Thanks, > | Paolo. > > I still consider talk of 'static_cast' in this context a non-starter. > However, maybe just saying "convert" would be OK -- though clearly > giving hints of dynamic_cast is much better. To be clear, currently we do *not* talk of static_cast, likewise the other compilers I have access to. We say "cannot convert ...". > Minor nits: say "base class" instead of "base", and "derived class" > instead of "derived type". I see, I wondered whether that would be better. > Otherwise, patch OK with these suggestions. Great, thanks a lot. Paolo.
On 07/05/2013 08:36 AM, Gabriel Dos Reis wrote: > I still consider talk of 'static_cast' in this context a non-starter. > However, maybe just saying "convert" would be OK -- though clearly > giving hints of dynamic_cast is much better. I wouldn't mind mentioning dynamic_cast, along the lines that Gaby suggested in the PR. Jason
Hi, Jason Merrill <jason@redhat.com> ha scritto: >I wouldn't mind mentioning dynamic_cast, along the lines that Gaby >suggested in the PR. Sure, but let me think about it, because isn't immediately obvious (to me at least!) *when* that would really help. Paolo
Index: cp/class.c =================================================================== --- cp/class.c (revision 200681) +++ cp/class.c (working copy) @@ -291,9 +291,31 @@ build_base_path (enum tree_code code, if (code == MINUS_EXPR && v_binfo) { if (complain & tf_error) - error ("cannot convert from base %qT to derived type %qT via " - "virtual base %qT", BINFO_TYPE (binfo), BINFO_TYPE (d_binfo), - BINFO_TYPE (v_binfo)); + { + if (SAME_BINFO_TYPE_P (BINFO_TYPE (binfo), BINFO_TYPE (v_binfo))) + { + if (want_pointer) + error ("cannot convert from pointer to base %qT to pointer " + "to derived type %qT because the base is virtual", + BINFO_TYPE (binfo), BINFO_TYPE (d_binfo)); + else + error ("cannot convert from base %qT to derived type %qT " + "because the base is virtual", BINFO_TYPE (binfo), + BINFO_TYPE (d_binfo)); + } + else + { + if (want_pointer) + error ("cannot convert from pointer to base %qT to pointer " + "to derived type %qT via virtual base %qT", + BINFO_TYPE (binfo), BINFO_TYPE (d_binfo), + BINFO_TYPE (v_binfo)); + else + error ("cannot convert from base %qT to derived type %qT via " + "virtual base %qT", BINFO_TYPE (binfo), + BINFO_TYPE (d_binfo), BINFO_TYPE (v_binfo)); + } + } return error_mark_node; } Index: testsuite/g++.dg/inherit/virtual10.C =================================================================== --- testsuite/g++.dg/inherit/virtual10.C (revision 0) +++ testsuite/g++.dg/inherit/virtual10.C (working copy) @@ -0,0 +1,11 @@ +// PR c++/14263 + +struct A { }; + +struct B : virtual A { }; + +int main() +{ + A* p = new B; + B* q = static_cast<B*>(p); // { dg-error "cannot convert from pointer to base 'A' to pointer to derived type 'B' because the base is virtual" } +}