Re: suprise with -=

[Ray Andrews <rayandrews@eastlink.ca>]

On 10/19/2015 11:35 AM, Bart Schaefer wrote:
> On Oct 18, 10:46pm, Ray Andrews wrote:
> }
> } That's a bit of a surprise, why is zsh fussier with '-=' than with '+='?
>
> Outside of the (( )), -= is not an assignment operator at all, because
> the default is to do either array or string assignment, and there is
> no sensible way to "subtract" one array or string from another.
>
> Conversely += is defined to mean "append", so it is a valid operator.
>
> I'd almost call it a bug that [outside of (( )) context] first+=second
> does arithmetic when $first is an integer.  It ought to be either an
> error or forcibly convert $first to string and append "second".
I've managed to suppress my gag reflex with all that arithmetic 
stuff--goes back to
the need to declare variable types, which is what I'm trying to do with 
'integer' and
after that I'd expect both increment and decrement to behave the same 
way.  I see
what you mean tho--we can append strings but we can't un-append them 
(tho one
might consider that as  " first=${first%$second} " (not sure if I wrote 
that right, but you
get me) ).  For now I feel comforted to always use the (( )) because 
it's explicit and you
can mercifully space things:  (( first -= second )).  Just to comment, 
I'd consider it
very rude for any forcible conversions to occur.  Better an error, tho 
again once one
has declared an integer one might expect one's operators to behave 
consistently.
We don't have warnings do we?  In C, of course, if one is doing 
something strange
the compiler doesn't stop you, but it will warn you.  I once had great 
fun writing an
encrypt function that performed arithmetic on strings--the compiler 
didn't like it,
but it did what it was told. Na ... can't have warnings in interpreted 
stuff, tho
there could be a proofreader ...