Q. Is local a bad part in Perl?
A. In my opinion, Yes. local is a bad part in Perl. If I could re-implement Perl, I will not implement local.
local $foo;
Q. Why does local a bad part?
A. This is because the variable that is the operand of local is a global variable although at a glance it looks like a local variable in C.
int32_t foo;
Q. What should be used instead of local?
Using my in all Perl programs is recommended strongly.
my $foo;
This is called a lexical variable. This is strange name we don't usually hear in daily life.
Q. Does local need to be used in current days.
Q. I want to say No, but in some cases, local is used in current days. One is to save and restore predefined global variable.
{
# Save
local @ARGV;
}
# Restore @ARGV at the end of the scope
Tow is to get the whole content of a file.
my $content = do { local $/; <$fh>; };
Ugly, user experience is worse than other programing languages, but most efficient way because Perl doesn't have the function to get the whole content of a file.
The efficient is sacrificed, the following code can be written.
my $content = join('', <$fh>);
Q. Are there ways to restore lexical variables?
Yes, using Scope::Guard.
Top comments (4)
I generally use it if I want to temporarily over-ride a function:
{
local *Foo::Bar::baz = sub { ... };
...
}
It's far more convenient than saving, over-riding, and restoring, and also guarantees that the restore actually happens even if an exception means that the end of the block is never reached.
Thank for telling a local usage!
You didn't mention usage like
local delete $hash{key}orlocal $hash{key} = 'yadayada'which is convenient and more expressive than using of guardsOK. About the usage, the problem seems to be only naming.