Re: vectors are something else

[Daniel Hartwig]

On 15 April 2013 19:29, Daniel Llorens <address@hidden> wrote:
>
> [1] have vector- ops only accept vector- types. …
>
> [2] force all vector objects into arrays. …
>
> For example in [1], you'd prefer vector- to *reject* strided rank-1 arrays
> (inc!=1), because those require a descriptor and you want to limit your
> checks to is-this-scm_tc7_vector.

Though such an array is potentially still a vector according to the simple
explanation in the manual.  So this requires introducing a more
complicated discussion of when is an array a vector.  And a lot of the
uses for treating some arrays as vectors will be lost with this, as it
quite restrictive on the layout of the source data.

Given the semantic complications and lesser utility, it may as well be
that no vectors are arrays and reject all.

> On the other hand, in [2],
> you want to *accept* offset rank-1 arrays (lbnd!=0) because to
> reject them you need an explicit check and it's faster to just do
> the index computation with this lbnd.
>

In this case, ‘vector?’ still must answer #f as the offset indexing
makes the object not a vector.  Right?

Most non-vector objects passed to ‘vector-ref’ will throw an error,
except for offset arrays.  Since the result is unspecified aka “it is
an error”, it doesnt have to be correct (ie. include lbnd).  Is it
really much faster to do one or the other:

 if lbnd != 0: error
 index = …

vs:

 index = lbnd + ...

?