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Answer: Subroutine args by-value vs. by-ref

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Q&A > subroutines > Subroutine args by-value vs. by-ref contributed by wog

The implict reference is not a hard reference, as perlref speaks of, but an aliasing that occurs. For example:

sub x { $_[0] = "in x"; } my $foo = "outside"; x($foo);
... will set $foo to "in x". The thing in @_ has become an alias for $foo. However, you won't get this behavior if you explictly copy the value out of @_, as in:
sub x { my($foo) = @_; $foo = "in x"; } my $foo = "outside"; x($foo);
When you copy the value, you are not working with an alias to the thing passed in, but you a working with a copy, bringing you the pass-by-value semantics that are probably more intutitive to you.

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