Re: More subfunction scoping issues.

[David Bateman]

John W. Eaton wrote:
> On 30-Mar-2007, David Bateman wrote:
>
> |  What would be needed to fix this issue, as I've
> | just been given a large chunk of matlab code that relies on these
> | scoping rules?
>
> If your code is not too complex, then you can change it from
>
>   function f ()
>     v1 = ...;
>     g ()
>     ## ... use modified v1 here ...
>     function g ()
>       v1 = ...;
>     end
>   end
>
> to
>
>   function f ()
>     v1 = ...;
>     v1 = g (v1)
>     ## ... use modified v1 here ...
>   end
>   function v1 = g (v1)
>     v1 = ...;
>   end
>
> Or, if the nested functions don't actually modify the variables they
> inherit from the parent, you can omit the output parameters from the
> new subfunctions.
>
> If the code you were given is large and has many variables, then this
> transformation will be somewhat hard to do unless you understand the
> code very well.
>
> If the code you have is complex and has many variables shared between
> the parent and nested functions, then I think that as you have to
> modify the code you will discover that nested functions are a really
> bad idea for a language like the one used by Octave.  The problem is
> that you have no way of declaring that a variable is local to a
> subfunction and NOT inherited from the parent environment.  That makes
> the new scoping rules a code maintenance disaster waiting to happen.
> Sure, it is easy to see what might be happening in a simple set of
> nested functions with just a few lines of code and variables, but if
> you have anything larger than a page or so, then I think you will have
> trouble.  It is just too easy to introduce a variable in a nested
> function that unintentionally changes the value of a variable in a
> parent function.  To be sure that you are not screwing something up,
> you need to know the names of all the variables used in the parent
> function.  This problem could maybe be solved by introducing the
> notion of local variables, but without local variables, I think nested
> functions are unusable for anything more than trivially small example
> programs.
>
> jwe
>
>   
I kind of agree, but having different scoping rules certainly makes
sharing code a bit harder.. Thanks for the advice..

Cheers
David

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