Re^3: local variable syntax

Well, I said "basically" never. Like all blanket statements, there are exceptions. Perhaps I should have said: Use my by default, use local when you understand why you can't use my in a specific situation. You can create 'stack-like' aggregates with local as you demonstrate, but you need a very good reason.

# some good reasons:

# if you modify a side-effect global like $/, 
# do it in the smallest scope possible:
my $slurped = do { local $/; <$some_Fhand> };

# override an element of a global aggregate in a 
# limited scope:
{
   local $SIG{"ALRM"} = \&some_handler;
   alarm $timeout;
   some_action();
}
[download]

Of course, I agree that understanding the difference is much better than applying a blanket maxim. (Which is why I pointed to an article that does just that.)

Comment on Re^3: local variable syntax Select or Download Code

Replies are listed 'Best First'.
Re^4: local variable syntax by jdporter (Paladin) on Apr 07, 2011 at 16:54 UTC
Like all blanket statements, there are exceptions. But these aren't even exceptions. They are simply other first-class cases. Perhaps I should have said: Use my by default, use local when you understand why you can't use my in a specific situation. That would certainly be better, but, like your previous post, it begs the usage context. Which is, namely: When you want to declare a variable. `local` is not good for declaring variables. In fact, it simply does not do that at all! What it does (and this was pretty much your first and only line of defence in Perl 4) is let you safely use a prior existing global variable in your "private" scope. As long as all scopes follow the protocol of localizing their variables before use, global variables can work fine. But that's a big "if", and lexical variables (introduced in Perl 5) allow a great measure of safety which doesn't even depend on every scope abiding by the rules. I reckon we are the only monastery ever to have a dungeon stuffed with 16,000 zombies.	[reply]

Replies are listed 'Best First'.

Re^4: local variable syntax
by jdporter (Paladin) on Apr 07, 2011 at 16:54 UTC

Like all blanket statements, there are exceptions.

But these aren't even exceptions. They are simply other first-class cases.

Perhaps I should have said: Use my by default, use local when you understand why you can't use my in a specific situation.

That would certainly be better, but, like your previous post, it begs the usage context. Which is, namely: When you want to declare a variable. local is not good for declaring variables. In fact, it simply does not do that at all! What it does (and this was pretty much your first and only line of defence in Perl 4) is let you safely use a prior existing global variable in your "private" scope. As long as all scopes follow the protocol of localizing their variables before use, global variables can work fine. But that's a big "if", and lexical variables (introduced in Perl 5) allow a great measure of safety which doesn't even depend on every scope abiding by the rules.

I reckon we are the only monastery ever to have a dungeon stuffed with 16,000 zombies.

[reply]