I know about generic lambdas , and I know about variable templates, but, what does this do? Is it even allowed?
template<typename T>
auto f = [](auto a, T b){ /**/ };
If it's allowed, can it be used as expected? That is, as f<type>(var_a, var_b)
?
A variable template must be declared constexpr
. A lambda cannot occur in a constant-expression , so the initialisation is not allowed, and its operator()
is not declared constexpr
, so calling it isn't allowed.
In summary, this is ill-formed in the current C++14 draft.
Note: curiously, even though a lambda-expression cannot occur in a constant-expression , it seems that the closure type of a lambda may have a constexpr
copy/move constructor.
该代码现在在C ++ 14的当前草案中是合法的,并且可以使用clang 3.5 trunk进行编译
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