why the fourth of these examples is an error

I'd say it's in accordance with strict (emphasis mine):

strict vars

This generates a compile-time error if you access a variable that was neither explicitly declared (using any of my, our, state, or use vars ) nor fully qualified.

(Edit: to re-phrase, maybe it's more clear -- was neither explicitly declared nor is fully qualified.)

Thus, no surprise that next 2 lines fail:

perl -wMstrict -e "$::x=0; $x++"                        # not OK
perl -wMstrict -e "package foo; $foo::x=0; $x++"        # not OK

[download]

Next 2 lines are your examples -- it's strange 2nd (your third) doesn't fail:

perl -wMstrict -e "BEGIN{*::x=\$a} $x++"                # not OK (1)
perl -wMstrict -e "BEGIN{package foo; *::x=\$a} $x++"   # OK     (2)

[download]

It has something to do with BEGIN:

perl -wMstrict -e "{package foo; *::x=\$a} $x++"        # not OK

[download]

the deparsed output is an insult:

C:\>perl -MO=Deparse -wMstrict -e "{package foo; *::x=\$a} $x++"
Variable "$x" is not imported at -e line 1.
Global symbol "$x" requires explicit package name (did you forget to d
+eclare "my
 $x"?) at -e line 1.
-e had compilation errors.
BEGIN { $^W = 1; }
use strict;
{
    package foo;
    *main::x = \$a;
}
$main::x++;

[download]

But also with "main" package. Next 2 are symmetrical with examples (1) and (2), just with "bar" instead of "main", but both OK now:

perl -wMstrict -e "BEGIN{package bar; *bar::x=\$a} package bar; $x++" 
+  # not OK
perl -wMstrict -e "BEGIN{package foo; *bar::x=\$a} package bar; $x++" 
+  # OK

[download]

Edit 2: Actually, replacing "main" with "bar" doesn't change anything (fixed one of the lines above).

In reply to Re: Logic for importing and strict vars? by vr
in thread Logic for importing and strict vars? by haukex

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