I have very strange (quantum-like: looking at a variable causes it to exist with the right value!) behavior, which I am sure must be documented somewhere deep in the perl documentation.

I can't replicate it in any small program, so I will describe the behavior here.

Update: see my reply to myself, where a small program to replicate this behavior is shown

A package I have reads: 

...
my $var
...
sub initialize
{ ...
  $var = 'this string';
  ...
}

sub mysub
{
    # print STDERR "var = $var";
    print STDERR eval("...$var...");
}

BEGIN { initialize() }

[download]
gives me: Use of uninitialized value in concatenation (.) or string at (eval 40) line 1. but if I uncomment the print line, everything works fine, and 'this string' prints out with no errors at all!

It is a large, spaghetti of a program, but I have verfied that deleting the one comment character produces this result.

I know that looking at a variable can cause it to get defined, but how can a simple print cause an unitialized variable to get defined with the right value?

In reply to quantum behavior in perl? by b4swine

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