Cleaner code is: 
sub is_readonly {
    eval {my $save=$_[0]; $_[0]=$save;};
    return $@ =~/read.?only/;
}

[download]
Scalar::Util did not work for me.

In reply to Re^2: How could I check if a variable is 'read-only'? by lifeboat
in thread How could I check if a variable is 'read-only'? by vladb

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