https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93906
Bug ID: 93906
Summary: Add front end support for std::conditional<Cond, T,
F>::type
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
As detailed in
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1715r0.html there are
significant compile-time costs to heavy use of std::conditional.
The Microsoft compiler treats the std::conditional class template as a built-in
type and expands std::conditional<true, T, F>::type to the type T, and
std::conditional<false, T, F>::type to the type F, without actually
instantiating the class template. This is anecdotally reported to be a huge
advantage for compile times.
Implementing a similar feature in G++ would benefit both libstdc++ and user
code, and remove my motivation to replace most uses of std::conditional in
libstdc++ code.
