Lambda idioms

Closures replace functor classes; the IIFE idiom initializes complex consts in one expression.

const auto table = [] {
  std::map<int, std::string> m;
  for (int i = 0; i < 8; ++i) m[i] = name(i);
  return m;
}();   // IIFE: complex const init

Generic lambdas and init-captures: move state in, take auto&&, forward on. Lambdas become the default function objects of generic code.

auto task = [buf = std::move(buffer)](auto&& sink) {
  sink.write(buf);
};

constexpr by default where possible; *this captured by value for async member work.

Template parameter lists on lambdas, lambdas in unevaluated contexts, and default-constructible stateless lambdas — a lambda type can now be a comparator template argument directly.

auto by_name = [](const auto& a, const auto& b){ return a.name < b.name; };
std::set<Person, decltype(by_name)> s;        // no constructor arg needed

Deducing this enables natural recursion (the lambda names itself); static operator() removes the unused this from stateless call operators.

auto fib = [](this auto self, int n) -> long {
  return n < 2 ? n : self(n - 1) + self(n - 2);
};

Stable feature-wise; reflection can inspect closure types, but day-to-day lambda idioms are considered finished.

Nothing in flight that changes lambda guidance.