Is substitution failure an error with dependent non-type template parameters?

Question

Let\'s say I have these template aliases:

enum class enabler {};

template 
using EnableIf = typename std::enable_if::         


        

Answer 1

^{First and foremost, thanks to @Richard Smith on the #llvm IRC Channel on oftc for the explanation.}
Unfortunately, this is not legal C++ and as such Clang is correct: {} is not an expression but a braced-init-list and as such will never be a constant expression as is needed in the initializer of a non-type template parameter.

§14.3.2 [temp.arg.non-type] p1

A template-argument for a non-type, non-template template-parameter shall be one of:

• for a non-type template-parameter of integral or enumeration type, a converted constant expression (5.19) of the type of the template-parameter; or
• [...]

One solution would be a dummy value in enabler.