Re: [boost] [boost.process] 0.6 Redesign

Subject: Re: [boost] [boost.process] 0.6 Redesign
From: Klemens Morgenstern (klemens.morgenstern_at_[hidden])
Date: 2016-04-19 14:51:52

Am 19.04.2016 um 20:08 schrieb Niall Douglas:
> On 19 Apr 2016 at 13:34, Klemens Morgenstern wrote:
>
>> Because it absolutley requires
>> metaprogramming and it is the only elegant choice. On Windows you have a
>> function overblown with parameters, making it unreadable. On Posix you
>> have to call several functions to get a process up. And my design has a
>> variadic function, which allows you to pass only the arguments you need.
>
> A freeform constructor with tagged parameters is absolutely right for
> when the parameters can be extended by third party code. Here though
> parameter types are completely known, so the appropriate design for
> when there are too many parameters and/or you'd like to name them is
> to pass a tagged tuple aka a struct.
>
> The choice to use metaprogramming should always confer an absolute
> design win over all other design alternatives given the increased
> compile times, memory usage, brittleness and other factors.
> Metaprogramming is very much not free of cost. It should be used as
> sparingly as possible in publicly facing library APIs.
>
> In particular I find Process' use of a freeform constructor
> gratuitous given the much simpler close substitutes like passing a
> struct.
>

Well, it doesn't seem like we'll agree any time soon, but that's imho 
the beauty of open-source. If you have any design for a process library, 
I would be very much interested in it.

Btw: boost.process 0.5 only allowed initializers to be passed to the 
execute function, i.e. you had to write

execute(set_exe("gcc"), set_args({"--version"});

I intentionally changed that, so one could write

execute("gcc", "--version");

because I find this much more intuitive (i.e. design win). This allows 
more parameter to be passed, like std::error_code or 
boost::asio::io_service. And unlike your proposed "make everything 
async" solution, you only pay for it, if you use it. I could add an 
exe_args initializer, so you can get rid of the initializer building 
altogether.

I personally consider the overhead reasonable, at least in comparison to 
forcing to much structure onto the user. And considering the amount of 
possible parameter you can pass, I'd think a struct would be rather 
incomprehensible.