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Re: C++ conversion rules ???
- To: Alexandre Oliva <oliva at dcc dot unicamp dot br>
- Subject: Re: C++ conversion rules ???
- From: Jason Merrill <jason at cygnus dot com>
- Date: 23 Jun 1999 00:54:39 -0700
- Cc: "Martin v. Loewis" <martin at mira dot isdn dot cs dot tu-berlin dot de>, ees1cg at ee dot surrey dot ac dot uk, egcs-bugs at egcs dot cygnus dot com, egcs-patches at egcs dot cygnus dot com
- References: <m10vgOP-0003JqC@ainur.ee.surrey.ac.uk> <199906201354.PAA00548@mira.isdn.cs.tu-berlin.de> <orbte75vaz.fsf@saci.lsd.dcc.unicamp.br>
>>>>> Alexandre Oliva <oliva@dcc.unicamp.br> writes:
> IMO, requiring the user to change his code, either by adding an
> explicit cast or an additional conversion operator, just to avoid this
> warning, is a very bad move.
>> Jason, can we please disable the warning, or make it conditional on a
>> flag?
> I vote for simply disabling it. Ok to install?
No. The warning is important; if your class has a conversion op that
converts to a type A, and another op which converts to type B which can
convert to A, you would expect that a cast to A would call the A operator.
But if it's const and the B one isn't, we end up going through the B op.
In the testcase we saw here, the two ops are identical, so there's no
problem, but if we're dealing with base & derived pointers, or a pointer
and bool, we're liable to run into significant problems.
The warning is there because the overload resolution rules are broken.
Jason