Howdy!

If you have long functions and long blocks, lots of other things go askew. Refactoring aggressively into shorter functions/methods/subroutines/whatever so that you can see the entire scope at once, just-in-time declarations are unremarkable. If you can't take the entire scope in at a glance, you do have to work harder to keep track of the matter.

Why do I like just-in-time declaration?

Consider

foreach my $foo (stuff)
{
    do stuff with $foo
}
[download]

Under most circumstances, $foo is meaningless outside the loop, so it makes sense to limit its scope to just the loop. Similarly, a variable used only within a block is best declared within that block so that it doesn't leak (for whatever useful sense of "leak" applies).

The real appeal is an application of the concept of "least privilege" (usually invoked in the context of security) to how large the scope of a variable needs to be. Less is more.

I was taking a stick to some code I inherited. The programmer was learning Perl on the fly and wrote a lot of C code in perl, without using strict or warnings. He did use "my" as he went along. I made it strict and warnings clean, but it was quaint, especially dealing with 1300 line routines. I applied "my" liberally. From time to time, I would get the complaint that a given variable was already lexical, but it did eventually yield the field to me...

I try to write short routines with variables' scopes as limited as I can make them.

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