I cannot compile a partial initialisation of a template [gcc 6.3.1]

[Georgios Petasis via gcc-help]

Στις 17/6/2017 01:22, ο Jonathan Wakely έγραψε:
> On 16 June 2017 at 22:44, Georgios Petasis via gcc-help
> <gcc-help@gcc.gnu.org> wrote:
>> Hi all,
>>
>> I am trying to compile the following code, I am getting an error, and I am
>> unable to fix the error.
>>
>> I am trying to compile this:
>>
>> template<typename Pattern>
>> class HasAttributeMatchingValue: public
>> AnnotationUnaryPredicateWithStates<std::string, Pattern> {
>>      bool operator() (const ELEP::CDM::Annotation& ann) const {
>>         return ann.containsAttributeMatchingValue(std::get<0>(m_state),
>> std::get<1>(m_state));
>>      };
>>   };
>>
>> The error I am getting is:
>>
>> `m_state` was not declared in this scope: return
>> ann.containsAttributeMatchingValue(std::get<0>(m_state),
>> std::get<1>(m_state));
>>
>> If I use instead:
>>
>> template<typename Pattern>
>> class HasAttributeMatchingValue: public
>> AnnotationUnaryPredicateWithStates<std::string, std::string> {
>>      bool operator() (const ELEP::CDM::Annotation& ann) const {
>>         return ann.containsAttributeMatchingValue(std::get<0>(m_state),
>> std::get<1>(m_state));
>>      };
>>   };
>>
>> It compiles without problem.
>>
>> AnnotationUnaryPredicateWithStates is a template:
>>
>> template<class... States> class AnnotationUnaryPredicateWithStates :
>>       public UnaryPredicateWithStates<ELEP::CDM::Annotation, States ... > {};
>>
>> template<class Arg, class... States> class UnaryPredicateWithStates :
>>       public UnaryFunctionWithStates<Arg, bool, States ... > {};
>>
>> template<class Arg, class Result, class... Ts>
>> class UnaryFunctionWithStates : public UnaryFunction<Arg, Result> {
>>      public:
>>         UnaryFunctionWithStates() = default;
>>         template <class... Args> UnaryFunctionWithStates(Args&&... args) :
>>              m_state(std::forward<Args>(args)...) {};
>>     protected:
>>          std::tuple<Ts...> m_state;
>>   };
>>
>> template<class Arg, class Result> class UnaryFunction {
>>      public:
>>         virtual Result operator()(const Arg &) const = 0;
>>   };
>>
>> What am I doing wrong?
> See https://gcc.gnu.org/wiki/VerboseDiagnostics#dependent_base
>
Dear Jonathan,

Thank you very much, this solved the problem. I didn't know about it.

Regards,

George