Re: octave 2.1.30 and example/make_int.cc

[John W. Eaton]

On 24-Apr-2000, address@hidden <address@hidden> wrote:

| However, I have two other questions things that are different
| in 2.1.30 than the last version I was using (2.1.19).
| 
| 1. Previously, you could access global configuration 
|    variables with Vprefer_column_vectors. That no
|    longer works.
| 
|    What is the new way to access global config vars?

You can still do that, I think, but Vprefer_column_vectors is now
static in ov.cc, so its scope is limited.  Can you explain why you
need access to this particular variable?

| 2. vector_value() method seems to have changed.
| 
|    previously, I wrote         
|          ColumnVector a = args(1).vector_value();
| 
|    however 2.1.30 gives the following error         
| 
|    make_sparse.cc: In function `class octave_value_list Fsplu(const class 
octave_value_list &, int)':
|    make_sparse.cc:1727: conversion from `Array<double>' to non-scalar type 
`ColumnVector' requested
| 
|    I now have to write
|          ColumnVector a = (const ColumnVector &) args(1).vector_value();
| 
|    it seems strange to have to cast a vector to a vector.         
|    Is there a new recommended method besides vector_value();

There are now column_vector_value and row_vector_value methods.  The
vector_value method returns an Array<double> object, so it is not
intended to have an orientation.

You can either fix your code to use column_vector_value (if you want
to force the user to supply a column vector) or use

  ColumnVector a (args(1).vector_value ());

if the row/column orientation of args(1) doesn't matter.  You don't
need a cast (though the ColumnVector constructor does perform a type
conversion).

If you find yourself frequently using casts, it probably means that
you are taking the wrong approach.  In the case above, you are casting
an Array<double> object to a ColumnVector object, which is derived
from MArray<double>, which is derived from Array<double>.  Casting in
that direction is bad news if the derived class adds new data (you are
lucky here that ColumnVector and MArray<T> do not add new data
members, but that is not always the way things work).

jwe



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