Dear Boost, I have been working on non-allocating future-promise which when combined with proposed expected<T, E> (i.e. basic_promise<expected<T, E>>) will provide a close substitute to std::future/promise, except that it doesn't use an allocator and can reduce to pure constexpr when possible e.g. this code: __attribute__((noinline)) int test1() { promise<int> p; auto f(p.get_future()); p.set_value(5); return f.get(); } ... reduces to exactly: _Z5test1v: # @_Z5test1v .cfi_startproc # BB#0: # %_ZN7promiseIiJEED2Ev.exit2 movl $5, %eax ret The non-allocating future-promise is intended to be compatible with the Concurrency TS extensions (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4123.html) where futures can have continuations scheduled against them via a future.then(callable). However, this involves an unavoidable memory allocation, which while fine for dynamically assigned continuations is overkill for statically assigned continuations. There is no reason why one could not also have a method of statically adding continuations which uses type extension to store the additions. Let us say we have a template<class T, class... Continuations> class promise and that this promise also provides a .then(callable) like this: template<class F> promise<T, Continuations..., F> then(F &&c) { return promise<T, Continuations..., F>(std::move(*this), std::forward<F>(c)); } ... and therefore to statically add continuations to the future promise, one simply iterates .then(callable) on the promise like this: auto p=promise<int>().then([]).then([]) ...; auto f=p.get_future(); p.set_value(5); // executes all the continuations My first question to the Boost community is this: is there some less ugly way? I'm thinking maybe the promise's constructor could take a set of continuations, and then a make_promise(callable, callable, ...) could construct a statically continued future-promise? My second question to the Boost community is this: should static continuations be able to see the value being set? Or indeed, to modify it before it gets sent to future.get()? My thanks in advance. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/