(This question is a branch-out from the discussion in the comments of Template specialization of variable template and type deduction.) [temp.expl.spec]/10 states that [emphasis mine]: A trailing template-argument can be left unspecified in the te...

[expr.unary.noexcept]的措辞在C ++ 20中已更改。 Previously (n4140, 5.3.7 noexcept operator [expr.unary.noexcept]), my emphasis: 如果在可能评估的上下文中表达式包含以下内容，则noexcept运算符的结果为false           （3.1）对函数，成员函数的潜在评估调用，     函数指针或不具有成员的成员函数指针     非抛出异常规范（[except.spec]），除非调用     是一个常...

Pardon my ignorance, it appears to me that std::array is meant to be an STL replacement for your regular arrays. But because the array size has to be passed as a template parameter, it prevents us from creating std::array with a size known only at runtime....