[boost] Re: N-arity operators in C++, also reducing temporaries. [Repost]

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2005-03-07 13:48:35

Pavel Chikulaev wrote:
> "Jonathan Turkanis" <technews_at_[hidden]> wrote in message
> news:d0hups$587$1_at_sea.gmane.org...
>> I'd like a library which simplifies the implementation of expression
>> templates.
>> However, I'd like it to be more general than you have outlined.
>
> More general? Plese tell me what you mean.

See my next comment.

>> For instance I
>> might not want a + -b to be computed as a - b, but I'd like to have
>> this as an option, and not just for this particular sequence of operations.
>
>     If you put LAZY_ALIAS(Matrix_ + -Matrix_ = Matrix_ - Matrix_) then
> a + -b will be computed as a - b, else it won't.

Okay, this certainly wan't clear from you're feature summary. I'll admit I
didn't study the sample usage; this was because the feature summary seemed
inadequate.

Now that I look at your sample, I wonder whether it is possible to support
operators which take instances of different types. This would be essential for
an expression templates library.

>> Also, I don't think it needs to be so heavily macro-based.
> The key feature of the library is to make library usage as simple as
> possible,

Of course.

> and macros is the only way (AFAIK) to achieve such simplicity.

> So, do you really think it can be less macro-based and
> more readable at the same time?
> If you have any ideas who do it, please send me how to do it.

Have you considered the approach taken by Boost.Operators?

   http://www.boost.org/libs/utility/operators.htm

Also, I believe Fusion (the sucessor to Tuple) would be a valuable tool.

I'm not saying that macros have no place in an expression templates library; in
the iostreams library, a single macro invocation is used to make a Filter usable
with operator|.

Jonathan