Re: [ublas] improve vector resize

From: Gunter Winkler (guwi17_at_[hidden])
Date: 2007-04-09 09:49:27

Am Montag, 9. April 2007 14:55 schrieb Neal Becker:

> Sorry, I'm not sure what you mean.  Do you mean that this only fixes
> vector<unbounded_array> and not other dense vector<storage...> ?

This fix applies of course for all storage types.

> I know, also matrix is not addressed.  My intention was to find out
> if we have some agreement that this is the preferred approach.  If
> there is some agreement, I'll try to provide a more complete patch.

We should update the container concept and the storage concept.

*From storage concept*

Resize 1:    a.resize(n, t)  

The container may be reallocated if its size changes. Existing element 
values are preserved, additional elements are copies of t.  

Resize 2:    a.resize(n)  

The container may be reallocated if its size changes. Element values are 
uninitialized. That is, each element value may be a previously assigned 
value or default constructed value for T. 

*From container concept*

Resize:      v.resize (n[, p]);

Erases or appends elements in order to bring the vector to the 
prescribed size. Appended elements copies of value_type(). When p == 
false then existing elements are not preserved and elements will not 
appended as normal. Instead the vector is in the same state as that 
after an equivalent sizing constructor.

*thoughts*

Before we update the code we should agree for a common concept.

About storage classes - We already have additionally to resize 1 and 2:

void resize_internal (const size_type size, const value_type init, const 
bool preserve);

So we could modify the resize-concept to be:

resize(n[, preserve = false[, init = false[, value = T()]]]);

The container may be reallocated if its size changes. The values of old 
elements are preserved if <code>preserve</code> is true. New elements 
are initialized with <code>value</code> if <code>init</code> is true. 
If <code>init</code> is false then new values are default constructed 
unless <code>detail::has_trivial_constructor&lt;T&gt;::value</code> is 
true.

<code>resize(n,t)</code> is the short form of 
<code>resize(n,true,true,t);</code>

What do you think?

mfg
Gunter