In essence, %sub_hash comes into being at the line where you declare it with my. And, if you did not take a reference to it, it would "go out of scope", that is to say, the space allocated to it would no longer be addressable when the subroutine ended. At this point, perl would know that nothing could reference that space and may choose to reuse that space for some other purpose sometime later.

However, as you have taken a reference to it and passed that reference back to an enclosing scope, (the calling program), perl has marked that peiced of storage as having been referenced and it therefore knows that it cannot reused that space until the variable holding the reference (and any other variables that it may have been assigned to) is itself no longer in scope at whatever level it was declared.

So, when you return a reference to space allocated at one level of program scope, to an enclosing level of scope, allthough you can no longer refer to it by the original name, you can still refer to it's memory via the reference and let Perl take care of the nitty-gritty of if and when that space can be freed for reuse elsewhere.

This comes as a strange concept if you have come from C or another language where you have to take care of allocating and deallocating storage yourself, but once you get used to it, it is an amazingly safe, powerful and useable concept.

Read this Lexical scoping like a fox several times carefully, and the concept may start to clarify. Enjoy.

Examine what is said, not who speaks.

In reply to Re: What's a reference? What's a variable? What's scope? by BrowserUk
in thread What's a reference? What's a variable? What's scope? by kurt_kober

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