Re: [boost] [xint] Boost.XInt formal review (concrete complaint)

Subject: Re: [boost] [xint] Boost.XInt formal review (concrete complaint)
From: Simonson, Lucanus J (lucanus.j.simonson_at_[hidden])
Date: 2011-03-06 20:43:15

Chad Nelson wrote:
> The only concrete complaint that people could give me about CoW was
> that code using it couldn't be made thread-safe, which is true. So I
> made a way to instruct the library to force all integer objects to
> have unique storage before they're returned to user code, and made it
> the default to prevent unpleasant client-code surprises. The internal
> code is single-threaded, and completely under my control in any case
> if I find it useful to make it multithreaded someday, so that
> answered the thread-safety complaint.
> 
> The only other complaints people had was that they didn't like it,
> which is not a valid reason to change it, and that move-emulation
> makes it irrelevant, which it doesn't in this case.

Chad,

This is not true, I made a concrete complaint about why I don't like COW or move-emulation for performance reasons.  

"
Pass by reference is what real programmers who deal and maintain real code do.  Rather that the false dicotomy between between COW and move lets answer the more fundamental question, why either?  Just use expression templates.  Don't bother to use proto for your expression templates, by the way, it is very easy to do yourself in this simple case.

This whole argument misses the point of optimizing code that uses a bigint class.  You want to reuse the memory allocated in a bigint variable over and over instead of reallocating every time.  Whether you make one unneeded allocation or two is a less important consideration than whether you make one or zero since 2/1 is a lot smaller than 1/0.  If a temporary is generated by the user's code they have already pessimized their code.  I am sorry, but you cannot avoid allocation with a return by value semantic, only expression templates allows you to reuse the storage on the left hand side of the assignment operator.  

Return by value is broken whether you use COW or MOVE so how about we focus on fixing it with a nice expression template based operator syntax using pass by reference and documentation that tells the user to avoid generating temporaries if they want to write code that will run as fast as possible.  If they want to write expressions that generate temporaries it will be *no slower* than the current proposal, but at least they will have the option of writing code that is fast.
"

Regards,
Luke