------- Comment #9 from jwakely dot gcc at gmail dot com 2009-08-05 10:03
-------
This example has four slightly different errors:
struct B {};
struct D : B {};
struct X {};
int foo(B*&);
int i = foo( (B*)0 );
int j = foo( (D*)0 );
D* pd = 0;
int k = foo( pd );
X* px = 0;
int l = foo( px );
GCC 4.4.1 gives:
pr13979.cc:8:20: error: invalid initialization of non-const reference of type
B*& from a temporary of type B*
pr13979.cc:6:5: error: in passing argument 1 of int foo(B*&)
pr13979.cc:10:20: error: invalid initialization of non-const reference of type
B*& from a temporary of type D*
pr13979.cc:6:5: error: in passing argument 1 of int foo(B*&)
pr13979.cc:13:17: error: invalid initialization of reference of type B*& from
expression of type D*
pr13979.cc:6:5: error: in passing argument 1 of int foo(B*&)
pr13979.cc:16:17: error: invalid initialization of reference of type B*& from
expression of type X*
pr13979.cc:6:5: error: in passing argument 1 of int foo(B*&)
Comeau gives equivalent errors in all four cases. The only significant
difference is that Comeau doesn't mention the types in the first two errors.
GCC 2.95.2 is quite different:
pr13979.cc:8: initialization of non-const reference type `struct B *&'
pr13979.cc:8: from rvalue of type `B *'
pr13979.cc:6: in passing argument 1 of `foo(B *&)'
pr13979.cc:10: initializing non-const `B *&' with `D *' will use a temporary
pr13979.cc:6: in passing argument 1 of `foo(B *&)'
pr13979.cc:13: initializing non-const `B *&' with `D *' will use a temporary
pr13979.cc:6: in passing argument 1 of `foo(B *&)'
pr13979.cc:16: type `B' is not a base type for type `X'
pr13979.cc:6: in passing argument 1 of `foo(B *&)'
I think the current diagnostics are better than the 2.95 ones. As I said
above, "will use a temporary" is misleading. The fourth error saying "is not a
base type" may be true, but is also misleading, because it wouldn't compile
even if it was a base type.
As I said earlier, it might be nice if the third error said e.g.
pr13979.cc:13:17: error: invalid initialization of reference of type B*& from
expression of type D*
pr13979.cc:6:5: error: in passing argument 1 of int foo(B*&)
pr13979.cc:13:17: note: conversion from `D*' to `B*' would create a temporary
However,
(In reply to comment #8)
> I don't even know if we have different codepaths for those!
if it's not possible then I think the current diagnostics are reasonable, and
at least as good as Comeau's.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13979
