Re: PATCH: += parameter assignments

[Oliver Kiddle <okiddle@xxxxxxxxxxx>]

> On Jan 14, 12:45pm, Oliver Kiddle wrote:

> The point is that I can't think of -anything- reasonable to expect,
> except perhaps that in a saner world ((s+=5)) would be an error
because
> you can't add an integer to a string.  Unfortunately we're beyond
hope
> of changing that (and I wouldn't really want to anyway).
>
> About the closest thing I can come up with is that all assignments in
> (( )) should force the parameter type to change to numeric (integer
or
> float), but that has its own set of potential gotchas.

This would seem sensible to me but is it too late to be changing that?
If you think it is an option then can you elaborate on the "gotchas"?

> Better might be if += outside of (( )) always converted numerics
> to strings and then did an append.

This is perhaps worth considering. I did actually consider it at the
time but didn't do it because of ksh compatibility. To be consistent
with assignments inside (( )), it would have the convert the result of
the appending back to a numeric type afterwards (which would limit the
usefulness of it).

> The argument is something like this:  It's OK for += to mean "convert
> to
> number, do arithmetic, then convert back to the original type" as
long
> as
> it *always* means that.  It's confusing when it means one thing in ((
> ))
> and two or more things (depending on the parameter type) outside ((
)).
>
> What I don't like is that I can't look at `s+=5' and know what it's
> going
> to do.  At least I know `((s+=5))' will always add 5 numerically,
even
> if
> it might convert s to 0 first.

But you can't look at s=foo and know what it is going to do because if
s is an integer, you end up with s being 0 (or whatever foo
arithmetically evaluates to). I think it would be better if this was a
scalar assignment but it isn't.

My intention was to never in a script use:
  numeric+=val using (( numeric+=val )) instead or,
  array+=val using array+=( val ) instead
so nobody reading the script might be confused.

Perhaps we could just make a recommendation in the manual that with
numeric variables assignments outside of (( )) not be used.

Note that David Korn included += in his "first cut" for the new
standard (item 48. in 3 Aug e-mail) so it might be worth sending him an
e-mail about this.

> To have -= be additive for strings and "subtractive" for numeric
types
> is just compounding the problem.

That probably just depends on how you think about the operations. `+'
being used as an appending operation seems fairly logical to me without
thinking about it as being "additive". `-' is the reverse of `+' and
prepending the reverse of appending so `-=' for prepending made sense
to me. I suppose I've used languages where `+' is a concatenation
operator quite a lot so am used to it. Anyway, I'm happy to accept that
it might seem less logical to other people and I won't be implementing
it now.

Oliver

__________________________________________________
Do You Yahoo!?
Everything you'll ever need on one web page
from News and Sport to Email and Music Charts
http://uk.my.yahoo.com