For the code below I get an ambiguous template instantiation error with gcc.However, using Clang or Visual Studio the Code compiles fine. A full working example of the code can be found here:http://coliru.stacked-crooked.com/a/60ef9d73ce95e6f9
I have a class template that is build from an aggegate type
template<template<typename...> typename AggregateType, typename ...>struct MyClass;The aggregate type is composed from a list of base classes, for example
template<typename ... Bases>struct Aggregate : Bases...{ };I have defined two specialzations of MyClass. The first specialization is the common case and reads
// specialization for two argument list for the// aggregate typetemplate<template<typename...> typename AggregateType, typename Base, typename ... Bases1, typename ... Bases2>struct MyClass< AggregateType, AggregateType<Bases1...>, AggregateType<Base, Bases2...>>{ void func() { std::cout << "not specialized\n"; }};A second specialization handels the case when the the second base list has only 1 argument
// specialization for the second argument list with length 1template<template<typename...> typename AggregateType, typename Base, typename ... Bases1>struct MyClass< AggregateType, AggregateType<Bases1...>, AggregateType<Base>>{ void func() { std::cout << "specialized\n"; }};Using MyClass with a second argument list of length 1, I expected the compiler to choose the second specialization of MyClass, since it is the more specilized template
class Foo {};class Bar {};int main(){ // this should give the not specialized class using NotSpecialized = MyClass<Aggregate, Aggregate<Foo, Bar>, Aggregate<Foo, Bar>>; NotSpecialized ns; ns.func(); // this should give the specialized class using Specialized = MyClass<Aggregate, Aggregate<Foo, Bar>, Aggregate<Foo>>; Specialized s; s.func();}While the code works fine with Clang, gcc gives an ambiguous template instantiation error. How can I circumvent this error and still use gcc?If I remove the AggregateType template argument, the code also works with gcc, see http://coliru.stacked-crooked.com/a/c1f6edd5fab7df4d