Alt text:
A screenshot from the linked article titled “Reflection in C++26”, showing reflection as one of the bullet points listed in the “Core Language” section
A screenshot from the linked article titled “Reflection in C++26”, showing reflection as one of the bullet points listed in the “Core Language” section
I can see the footguns, but I can also see the huge QoL improvement - no more
std::enable_ifspam to check if a class type has a member, if you can just check for them.… at least I hope it would be less ugly than
std::enable_if.You already can do that with C++20 concepts and the requires expression
template <typename T> concept has_member_foo = requires(T t) { t.foo(); }; // Will fail to instantiate (with nice error // message) if t.foo() is ill-formed template <has_member_foo T> void bar(T t) { // ... } // abbreviated form of above void baz(has_member_foo auto t) { // ... } // verbose form of above template <typename T> requires has_member_foo<T> void biz(T t) { // ... } // same as above but with anonymous concept template <typename T> requires requires(T t) { t.foo(); } void bom(T t) { // ... } // If already inside a function if constexpr (has_member_foo<T>) { // ... } // Same but with anonymous concept if constexpr (requires(T t) { t.foo(); }) { // ... }I imagine reflections would make the process more straightforward, requires expressions are powerful but either somewhat verbose or possibly incomplete.
For instance, in your example
foocould have any of the following declarations in a class:void foo();int foo() const;template <typename T> foo(T = { }) &&;decltype([]() { }) foo;There’s a pretty big difference though. To my understanding enable_if happens at compile time, while reflection typically happens at runtime. Using the latter would cause a pretty big performance impact over a (large) list of data.
C++26 reflection is compiletime