[ublas] Transition to default handling of possible lvalue aliases

From: Michael Stevens (mail_at_[hidden])
Date: 2005-06-17 08:35:03

Ok,

After Karl wrote

> Michael Stevens wrote:
> >I think Ian's suggestion of changing uBLAS default evaluation to be alias
> >unsafe and checking on DEBUG builds is the way to go!
> >
> >Michael
>
> I agree,

it would be good to try and agree on how we would make such a transition.

First we will need some syntax to tell uBLAS to expect the lvalue to be an 
alias of something on the RHS and so to use a temporary. My suggestion would
be to add the 'alias' function thus:
        alias (x) = expression;

This is equivalent to the current 'noalias' which can be dropped once the 
transition is complete.

Second we would need to document the expected change of semantics. The 
implementation of assignment without a temporary requires the lvalue be size 
conformant with the expression. This is different then the present default 
assignment via a temporary where we get resizing for free.

Would the change of semantics be a big problem for anyone?

Michael
-- 
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Michael Stevens Systems Engineering
34128 Kassel, Germany
Phone/Fax: [phone]
Navigation Systems, Estimation  and
                 Bayesian Filtering
    http://bayesclasses.sf.net
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