This will seem like a newbie RTFMish question at first, but it's slightly deeper than that. 
#I have a hash,

%myhash;

#I pass it by reference:

mergetwohashes(\%myhash, \%b);

sub mergetwohashes {
    my($a)=$_[0];
    my($b)=$_[1];
    $a = { %{$a},  %{$b} };
}

#After I call the function, %myhash is unchanged. Why.

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Note: I do NOT want to modify any keys of the passed in hash. (then it would be a newbie question). I'm trying to completely replace it with a totally new hash. I want to change the target of the reference, to a new hash.

I also tried derefencing it as if it was a scalar reference, but perl complains "not a scalar reference", as you might guess.

I also tried the method call like this:
mergetwohashes(%myhash, \%b);
mergetwohashes($myhash, \%b);

Just in case the backslash operator was doing something I didn't expect, but no.

Is this something deeper- does the Perl call stack not support this because the passed in @_ array is immutable? What's my workaround here?

thank you

In reply to Modify hash reference itself by Anonymous Monk

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