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!)
