Why does not a template template parameter allow 'typename' after the parameter list
Template template typename?
When using template template syntax as in template class T>, it is requi
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I'm looking for the rational behind this restriction [...]
Before C++11 was introduced, the only templates you could pass to a template template parameter were class templates. That's why the use of the keyword
classwas enforced. Additionally, the keywordtypenameimplies that the template parameter is a substitution for an arbitrary type and not a template, so usingtypenamein that context would just blur the line between the names of types and (class) templates. That's comprehensible.Nowadays, such arguments can be the names of class templates or alias templates, and since those aren't even remotely connected, the enforcement of the keyword
classis more or less obsolete. The proposal N4051 opts to change this with C++1Z.
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