Re: language inconsistency(wart) & RFE

[Linda Walsh]

Greg Wooledge wrote:
> On Sat, Oct 17, 2015 at 08:55:31AM -0700, Linda Walsh wrote:
> >         If I needed a way to declare something global, yes...
> > But what I am wanting is a way to allow changing the defaults
> > of the implicit variable creation (which could still be
> > explicitly declared with "-g" if one wanted their result to be
> > made global.
>
> So you are basically saying you want all of your function variables
> to be local
---
        No...  only ones where 'shopt -s auto_local' was in effect.

but you are too lazy to write 'local i j k' and you want
> bash to do it for you?
----
        local i j k doesn't define j as an array or k as a hash
or g (w/-g ) as a global or any case modification vars.
Not to mention your statement doesn't work:

function nint {
 local i j k
 for ((i=0; i<10; ++i)) ; do j+=i; k+=j ;done
 echo "i=$i, j=$j, k=$k"
}

> nint && echo "($i, $j, $k)"
i=10, j=iiiiiiiiii, k=jjjjjjjjjj
(, , )

You declared them all the same, but at the end of the
function, j and k do not have integer values.

Trying to init them:
function nint {            
 local i=0 j=0 k=0
 for ((i=0; i<10; ++i)) ; do
 j+=i
 k+=j
done
my -p i j k; echo "i=$i, j=$j, k=$k"
}
----
nint && echo "($i, $j, $k)"
declare -- i="10"
declare -- j="0iiiiiiiiii"
declare -- k="0jjjjjjjjjj"
i=10, j=0iiiiiiiiii, k=0jjjjjjjjjj
(, , )
---
Now we see that i & j & k all have the same
attributes ... yet only 'i' has an integer value.

If you could declare all the vars in 1 statement w/different types:

declare -i INT -a ARRAY -A HASH
---
That would be a huge improvement.  But instead,if you
use a 'for' statement, without pre-declaring all the vars
used, you end up leaking variables:

> function nint {            
for ((i=0; i<10; ++i)) ; do
j+=i                       
k+=j
done
my -p i j k; echo "i=$i, j=$j, k=$k"
}
> nint && echo "($i, $j, $k)"
declare -- i="10"
declare -- j="iiiiiiiiii"
declare -- k="jjjjjjjjjj"
i=10, j=iiiiiiiiii, k=jjjjjjjjjj
(10, iiiiiiiiii, jjjjjjjjjj)
---
"leaking variables" into the external environment
is almost always considered bad-practice.

The default that bash encourages with its default behavior
is for all implicitly used vars in a function to be
leaked to the global level.  From a program maintenance
and development standpoint, having such a horrible default
with no way to override it just seems really icky.











> Also I think you are completely misrepresenting the dynamic variable
> scope system that bash uses.  Variables are not just global or local.
> There's an entire stack of them.  When you reference a variable (let's
> say i) inside a function, bash searches up through the call stack
> looking for a variable named i until it finds one.
>
> Since functions cannot return values to their callers, the entire system
> of "put values into an upper-scope variable so the caller can see them"
> would break if your proposal of automatic localization were to be
> adopted.
>
>
> # Pick unbiased random number from 0 to N-1 ($1 = N)
> # Returns value in variable r.
> rand() {
>   local max=$((32768 / $1 * $1))
>   while (( (r=$RANDOM) >= max )); do :; done
>   r=$(( r % $1 ))
> }
>
> foo() {
>   local r
>   rand 6
>   echo "I rolled $((r+1))"
> }
>
> foo
> # r is not visible here
>
>
> Under your proposal, the variable r which is defined locally in foo, and
> is up-scope-visible to rand (so that rand can put a return value into
> it), would also be defined locally within r, so there would be no way to
> return a value from rand to foo.
>
> (If you want to attack "language warts", start with the inability to
> return values from functions to their callers!)