2021-03-12 · If the default is specified for a template parameter of a primary class template, primary variable template, (since C++14) or alias template, each subsequent template parameter must have a default argument, except the very last one may be a template parameter pack. In a function template, there are no restrictions on the parameters that follow a default, and a parameter pack may be followed by more type parameters only if they have defaults or can be deduced from the function

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