http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58119
Bug ID: 58119 Summary: Invalid ambiguous default type conversion with only a single invalid conversion listed. Product: gcc Version: 4.8.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: tilps at hotmail dot com 'Minimal' test case: template <class type> class Silly { public: Silly(type *value) { data_ = value; } operator type*() const { return data_; } template <class other> operator Silly<other>() const { return Silly<other>(data_); } private: type *data_; }; int main() { Silly<int> a(nullptr); delete a; } Fails giving: test.cc:20:10: error: ambiguous default type conversion from 'Silly<int>' delete a; ^ test.cc:20:10: error: candidate conversions include 'template<class other> Silly<type>::operator Silly<other>() const [with other = other; type = int]' test.cc:20:10: error: type 'class Silly<int>' argument given to 'delete', expected pointer I believe that this code should be considered valid, the only valid type conversion is via the operator type *() which then converts to void* for the delete operator. I don't see any way that Silly<anything> could be considered convertible, except via operator type *() - and as far as I was aware, only a single implicit cast operator is allowed to be considered in a type conversion chain. Interestingly, the valid type conversion is not mentioned as a candidate, and the candidate mentioned does not specify which template parameter type it would use for the 'other' template parameter. Ultimately this is a bit of a strange example - I was trying to resurrect some legacy code with a particularly dumb (but heavily used) 'smart pointer' type. But this code did work, at least as recently as 4.6 - and probably back before 3.2.