Re: [boost] Phoenix v3 review

Subject: Re: [boost] Phoenix v3 review
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2011-02-25 01:24:57

On Fri, Feb 25, 2011 at 7:08 AM, Joel Falcou <joel.falcou_at_[hidden]> wrote:
> On 25/02/11 03:21, Joel de Guzman wrote:
>>
>> :-) Mathias has a point. Let's also discuss this off-list. With Spirit,
>> I've already begun the migration towards an object free environment,
>> but that's for terminals --of which proto is known to slow down
>> compilation when there are lots of terminals. I am not quite sure
>> about function objects.
>
> I want to point you again tomy boostcon 2k10 talk. we showed figure where
> the old nt2, using instance of function object , resulted in a linear
> compile time,
> while having template function using make_expr get us constant compile time.
>
> Here the post I made way before on the same issue:
> http://lists.boost.org/boost-users/2009/02/45591.php
<snip>

You have a point for proto terminals. A phoenix::function is _not_ a
proto terminal though.
here is a sketch of the implementation:

template <typename Func>
struct function
{
    template <typename A0 ... typename AN>
    typename proto::result_of::make_expr<tag::function, Func, A0, ..., AN>
    operator()(A0 const& a0, ..., A1 const& a1) const
    {
           return proto::make_expr<....>(....);
    }
};

It already behaves like the proto generator functions you described.
Maybe the instantiation of a phoenix::function<F> also add
significantly to compile time and binary size. These were the numbers
I was interested in.