perlop - Assignment Operators may help. The assignment operator returns the object assigned to as an lvalue so your assignement and test is fine.

Update:

I'd be inclined to rewrite that as:

while ( $self ) {
  $path += $self->get_branch_length if $self = $self->get_parent;
}

return $path;

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DWIM is Perl's answer to Gödel

In reply to Re: assignment operator return values by GrandFather
in thread assignment operator return values by rvosa

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