Re: Can 'operator T const& () const' do any harm?
Alf P. Steinbach wrote:
However, this code:
class NoCopy
{
public: NoCopy() {}
private: NoCopy( NoCopy const& ); NoCopy& operator=( NoCopy const& );
};
class T: public NoCopy {};
void foo( T const& ) {}
int main() { foo( T() ); }
is accepted by two of the three compilers mentioned above; only g++
produces a compilation error (emits a diagnostic, barfs, whatever).
interesting issue. The code above is IMVHO valid, but it exploits loophole in
the standard. This loophole is entirely removed (and replaced with wide open
door) by resolution of CWG issue 391
To make the code compile also with g++ one possibility is to do
class T: public NoCopy
{
public: operator T const& () const { return *this; }
};
This is IMO bad from a design point of view, because it relies on
convention (having this repeated in every class).
But can it do harm, e.g. unintentionally allow something Bad, or
disallow something Good?
it will allow implicit conversion of your rvalues to lvalues (which IMHO is
bad) and make use of rvalue-references problematic once you port the code to
C++0x compliant compiler
B.
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