Function std::alloc_t

generic<T, A: Allocate> ?&heap T alloc_t(&A a)

One T / n Ts, aligned for T; null when the allocator can't. The memory is uninitialised. T is inferred from the target ('?&heap Packet p = alloc_t(&pool);'). alloc_array_t aborts with a diagnostic if n * sizeof(T) overflows (checked_mul_size).