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Re: conversions between vectors

Aldy Hernandez <> writes:

| >>>>> "Joseph" == Joseph S Myers <> writes:
|  > On 21 Dec 2001, Aldy Hernandez wrote:
|  >> "vector signed int".  Also, assignments between "signed int" and
|  >> "unsigned int" are allowed even in pedantic mode.  So, IMO the above
|  > And this (implict signed/unsigned conversions) is a source of security
|  > holes.

Completely agreed.

| But it follows C semantics.  You are allowed to copy signed int to
| unsigned int without any warnings of any kind.

Well, the C definition certainly allows a warning in such cases.


|  > The correspondence with valarrays was to some extent because those are a 
|  > well-developed set of semantics known to work.  Start by documenting in 
|  > the manual the correspondence with valarrays and, for C programmers, what 
|  > this means, and what parts of it are implemented.  Only then propose 
|  > specific extensions, with precise documentation for what they mean and 
|  > when they are allowed, and justification in each case.
| The correspondence is minimal IMO.

That correspondance is minimal only because you're insisting to keep
to separate, and to some extent incompatible implementations, for the
same concept.

|  Valarrays are vectors of any type
| (including arrays and aggregate types).  Vectors are merely vectors of
| the base types (char, int, short, float, double).

Err... Valarray<> are arrays of any type that *behaves like* fundamental

|  Valarrays allow
| overloaded arithmetic between them.  Vectors do not.

And it is questionnable why vectors should not.

|  Valarrays allow vectors of vectors.

Wrong.  Valarray< valarray<> > is formally prohibited.  However, I
made the extra effort to allow it because it was repeatedly requested
-- and I don't see any strong reason to disallow it.

|  Vectors do not.  Valarrays do not allow casts
| between vectors.  Vectors do.

And when they do, I suspect it construct a new vector.  But then in,
there is no real difference with respect to the machinery provided by
C++: You just invoke valarray<>::apply() withe the right functional
object. Or, you can std::trsnsform().

| Compatability with valarray is a nice thought, but I don't think it's
| quite relevant.

I disagree; compatibility with valarray<> is not a theoritical
issue. It stems from providing functionnalities we want to have in C
without dumping all the C++ features.

|  In documenting valarrays and C-vectors, we'll find
| more differences than similarities.

Then, feel free to raise the issue and I'll try to provide insites
based on my understanding of valarray<>.

-- Gaby

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