Perl doesn't (always) clear lexical variables with refcounts of zero at scope exit (it's an optimization).
Under normal circumstances, Perl always clears the variable; the optimisation is that it never frees it. The bug is that the run-time effect of of my is to push an instruction onto the savestack to clear the variable on scope exit. If the my is skipped, the var doesn't get cleared on scope exit, and its old value is still there at the next entry to the block. (Note that on entry to a block, my doesn't clear the variable).

Some people have used this as a way of getting static vars, but this is officially deprecated these days.

Dave.

In reply to Re^3: will you explain what's going on? by dave_the_m
in thread will you explain what's going on? by maard

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