[async.use.future.cons] says the default constructor is noexcept, but allocators are allowed to throw in their default ctor (see LWG 2455).
Currently if the allocator throws it would terminate, so if that's not acceptable then you could add a Requires saying the allocator constructor must not throw, or follow LWG 2455 and make it noexcept(noexcept(allocator_type())).
[async.use.future.cons] says the default constructor is
noexcept
, but allocators are allowed to throw in their default ctor (see LWG 2455).Currently if the allocator throws it would terminate, so if that's not acceptable then you could add a Requires saying the allocator constructor must not throw, or follow LWG 2455 and make it
noexcept(noexcept(allocator_type()))
.