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Subject: Re: [boost] [process] The Formal review preiod is nearing the end
From: Nat Goodspeed (nat_at_[hidden])
Date: 2016-11-07 16:14:53

On Mon, Nov 7, 2016 at 12:52 PM, Klemens Morgenstern
<klemens.morgenstern_at_[hidden]> wrote:

> Am 07.11.2016 um 21:09 schrieb Nat Goodspeed:

>> * any_initializer could still be used with any templated initializer
>> type. Isn't that still true?

> You're right, those were templated too. BUT the executor was actually not a
> template, so you could've written on_success(windows::executor& e). That is
> now different. I don't know how a type erasure could be done here, but I
> could write a variant.
> The reason is, that some properties/initializers require access the the
> sequence, mainly to obtain the reference of the io_service.

Please try that? I want a custom initializer to be able to access such
things too.

>> * Klemens states that the machinery needed to write custom
>> initializers is currently in the detail namespace. I want it to be
>> promoted out of the detail namespace: I want support for custom
>> initializers to be a documented, supported feature of the library. If
>> the library is not yet "done" in that respect, then let's consider it
>> again when it's more fully baked.

> Ok, so you have three things you can do: use custom handler for events, as
> in
> child c("foo", on_error([](auto & exec, const std::error_code &
> ec){std::cerr << ec.message() << std::endl;});
> which is already public & documented (or at least mentioned in the
> documentation).

I saw that, but was misled by the fact that the documentation showed a
nullary lambda.

In any case I'm more interested in a custom initializer that can
self-consistently intercept more than one such event.

> Secondly there is the basic inheritance of "handler"
> (currently private, but needlessly so)
> struct foo : boost::process::detail::handler
> {
> template<typename Exec>
> void on_error(Exec & exec, const std::error_code & ec)
> {
> std::cerr << ec.message() << std::endl;}
> };
> };
> foo f;
> child c("foo", foo);
> This has additional features like async_handler, where you can write an
> on_exit handler etc. and there's a function which get's the passed
> io-service; so it's a bit more rich than in 0.5.

Good! I think you're saying that this feature is stable? Let's just
move it out of "detail."

> Now the third option (and most complicated) would be that you declare a tag
> for a type, provide a builder and a initializer. I won't explain that here
> in detail, but let's say "foo" can be internally constructed from a sequence
> of "bar".
> The reason this is not public, is because I'm not sure what should be public
> and what not and I'm not sure if it works as a public interface the way it
> does internally. I think that needs some experience from someone other than
> me, actually implementing an extension, to know that. I didn't think that it
> would've been the best idea to put this in the version of the library to be
> reviewed, especially since I need the experience of someone else. I really
> think it makes much more sense to get the library accepted in its structure
> before we - and by we I mean me and a user, e.g. you, - work out the details
> of the public extension interface.

Then may I suggest a namespace like "experimental" (borrowing a
convention used in recent C++ documents)?

My expectation from other Boost libraries is that I am explicitly
supposed to avoid namespace "detail." The connotation is: hands off!

"experimental" suggests "API is still unstable" while leaving the
feature open for user testing.

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