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Subject: Re: [boost] Efficient tuple implementation
From: Larry Evans (cppljevans_at_[hidden])
Date: 2014-06-17 11:02:14

On 06/16/14 18:55, Louis Dionne wrote:
> Larry Evans <cppljevans <at>> writes:
>> On 06/15/14 08:44, Louis Dionne wrote:
>>> Larry Evans <cppljevans <at>> writes:
>>>> On 06/06/14 21:18, Louis Dionne wrote:
>>>>> [...]
>>>> IIRC, list uses an evaluator and "tagged" lists where the 1st element in
>> ^^^^ should be lisp
>>>> the list is a tag for the operation to be performed and the
>>>> evaluator dispatches on this tag to do the operation with the
>>>> operands being the remaining args in the list.
>>> I don't understand which list you are talking about.
>> OOPS. Very sorry for the typo above. I'm talking about
>> the language, Lisp:
>> and the pattern I was talking about was called "Polish
>> prefix notation" in the wikipedia article.
> Ok, now I understand better. As for your question, I did not follow the
> development of Spirit X3 close enough to know for sure. However, if you
> have to store variadic arguments, using a lambda somewhere in there is
> probably the most efficient way. And as soon as you have stuff in a
> variadic representation, it's better if you keep it that way because
> most algorithms will perform better on variadic packs.
> The way I see it for Boost.Hana, your dispatching system could be used
> internally as an optimization to dispatch efficient operations on variadics,
> while keeping the more flexible type class based dispatching interface. I'll
> keep that on the back of my head for when I start optimizing seriously.
> Thanks,
> Louis

A more complete example, which uses operators || and && to create the
tagged tuples, is now here:

The use of the operators make it more like what spirit does with, for
example, operators | and >>.

However, I still don't have a good idea of how useful this will be.
Only more experimentation can tell.

Hopefully others may have some ideas on how to use this.


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