In: struct bar {}; void foo1() { bar& b = bar(); } void foo(bar& b = bar()) {} you get: ~/ootbc/members/src$ g++ foo.cc foo.cc: In function `void foo1()': foo.cc:3: error: invalid initialization of non-const reference of type 'bar&' from a temporary of type 'bar' foo.cc: At global scope: foo.cc:5: error: default argument for `bar&b' has type `bar' for essentially the same error. The second diagnostic is distinctly inferior Ivan
Comeau gives: Comeau C/C++ 4.3.3 (Aug 6 2003 15:13:37) for ONLINE_EVALUATION_BETA1 Copyright 1988-2003 Comeau Computing. All rights reserved. MODE:strict errors C++ "ComeauTest.c", line 3: error: initial value of reference to non-const must be an lvalue bar& b = bar(); ^ "ComeauTest.c", line 5: error: initial value of reference to non-const must be an lvalue void foo(bar& b = bar()) {} ^ 2 errors detected in the compilation of "ComeauTest.c". IMHO this is better than the second and worse than the first that gcc gives.
Confirmed.
Author: jason Date: Wed May 14 16:48:07 2014 New Revision: 210436 URL: http://gcc.gnu.org/viewcvs?rev=210436&root=gcc&view=rev Log: PR c++/20332 PR c++/21631 * call.c (reference_binding): Treat lvalue/rvalue mismatch and dropped cv-quals as a bad conversion. (convert_like_real) [ck_ref_bind]: Explain them. (compare_ics): Check badness before stripping reference bindings. Handle comparing bad reference bindings. * typeck.c (comp_cv_qualification): Add overload that just takes integers. * cp-tree.h: Declare it. Added: trunk/gcc/testsuite/g++.dg/cpp0x/diag2.C trunk/gcc/testsuite/g++.dg/diagnostic/ref1.C trunk/gcc/testsuite/g++.dg/diagnostic/ref2.C Modified: trunk/gcc/cp/ChangeLog trunk/gcc/cp/call.c trunk/gcc/cp/cp-tree.h trunk/gcc/cp/typeck.c trunk/gcc/testsuite/g++.dg/conversion/op4.C trunk/gcc/testsuite/g++.dg/cpp0x/overloadn.C trunk/gcc/testsuite/g++.dg/expr/cond9.C trunk/gcc/testsuite/g++.dg/init/synth2.C trunk/gcc/testsuite/g++.dg/lookup/two-stage4.C trunk/gcc/testsuite/g++.dg/overload/arg3.C trunk/gcc/testsuite/g++.dg/overload/conv-op1.C trunk/gcc/testsuite/g++.dg/overload/copy1.C trunk/gcc/testsuite/g++.dg/overload/volatile1.C trunk/gcc/testsuite/g++.dg/rtti/dyncast6.C trunk/gcc/testsuite/g++.dg/template/copy1.C trunk/gcc/testsuite/g++.old-deja/g++.benjamin/15800-1.C trunk/gcc/testsuite/g++.old-deja/g++.brendan/cvt3.C trunk/gcc/testsuite/g++.old-deja/g++.bugs/900514_03.C trunk/gcc/testsuite/g++.old-deja/g++.eh/ctor1.C trunk/gcc/testsuite/g++.old-deja/g++.jason/temporary2.C trunk/gcc/testsuite/g++.old-deja/g++.law/cvt20.C trunk/gcc/testsuite/g++.old-deja/g++.law/enum4.C trunk/gcc/testsuite/g++.old-deja/g++.law/init8.C trunk/gcc/testsuite/g++.old-deja/g++.law/operators9.C trunk/gcc/testsuite/g++.old-deja/g++.mike/net8.C trunk/gcc/testsuite/g++.old-deja/g++.mike/p1989.C trunk/gcc/testsuite/g++.old-deja/g++.mike/p2431.C trunk/gcc/testsuite/g++.old-deja/g++.mike/p438.C trunk/gcc/testsuite/g++.old-deja/g++.mike/p701.C trunk/gcc/testsuite/g++.old-deja/g++.other/crash24.C trunk/gcc/testsuite/g++.old-deja/g++.other/volatile1.C trunk/gcc/testsuite/g++.old-deja/g++.pt/auto_ptr.C trunk/gcc/testsuite/g++.old-deja/g++.pt/t05.C trunk/libstdc++-v3/testsuite/20_util/forward/1_neg.cc
Fixed on trunk.