Re: [Boost-users] [multi_array] operator= requires resize - why?

From: Matthias Troyer (troyer_at_[hidden])
Date: 2007-01-16 15:51:58

On Jan 16, 2007, at 4:59 PM, Ronald Garcia wrote:

> Hello Markus,
>
> On Jan 16, 2007, at 9:06 AM, Markus Werle wrote:
>
>> IMHO the behaviour of operator= for multi_array is a little bit
>> broken.
>> A lot of preconditions required:
>
> Indeed operator= for multi_array requires the sizes of the
> multi_arrays to match, hence the assertions.  The multi_array type is
> not meant to automatically resize when assigned to.  All resizing is
> intentionally meant to be explicit.
> For your application, you will need to resize your array prior to
> assignment.

This is awkward since it means that any class with a multi_array  
member cannot use the default operator= but needs to implement a  
special operator=. We just ran into a subtle bug with this because of  
the semantics of the valarray operator=, and I would strongly argue  
for an operator = that makes the semantics of

A x = y;

equivalent to

A x;
x = y;

Matthias