++ to your explanation. Brings to mind a post of mine from long ago where someone alerted me to the different program execution phases that variable declaration and variable assignment happen in. It was new to me then.

I am curious about your comment regarding the "copy constructor technique" - I assume you mean a constructor snippet like: 

sub new{
   my $proto = shift;
   my $class = ref($proto) || $proto;
   bless {}, $class;
}

[download]
I am curious because I vaguely recall some prior nodes deriding this practice, mostly as I recall claiming that it's cargo-cult coding and the person writing the code doesn't understand what it does. But what makes you say that this usage is almost always an error? As long as you understand what it does, it seems like an acceptable shortcut to object instantiation, although I personally wouldn't use it. Is there some hidden danger here that I don't know about? If I remember correctly, my (outdated) edition of The Camel uses code like this.

In reply to OT: copy constructor by crashtest
in thread scope and declaration in local packages by december

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