BIND 10 #2565: Refactor RR param parsing code in MasterLoader

[BIND 10 Development]

#2565: Refactor RR param parsing code in MasterLoader
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            Reporter:  muks          |                        Owner:
                Type:  enhancement   |  jinmei
            Priority:  medium        |                       Status:
           Component:  libdns++      |  reviewing
            Keywords:                |                    Milestone:
           Sensitive:  0             |  Sprint-20130108
         Sub-Project:  DNS           |                   Resolution:
Estimated Difficulty:  0             |                 CVSS Scoring:
         Total Hours:  0             |              Defect Severity:  N/A
                                     |  Feature Depending on Ticket:
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Changes (by muks):

 * owner:  muks => jinmei


Comment:

 Hi Jinmei

 I have prepared the branch using `boost::optional` as you have
 recommended, but I think it is not necessary in this case.

 * The bare version (returning `NULL` instead of `MaybeRRClass()`) that we
 talked about on Jabber seems to be enough for this particular case. The
 current code in the branch (with `MaybeRRClass`) has the same effect in
 our use-case.

 * Even in the RRTTL case, using `MaybeRRTTL` may not need additional
 allocation but does the caller not do an object copy which seems to defeat
 this optimization? Is introducing `boost::optional` required?

 * Our use of `boost::optional` does not seem to match the purpose it was
 written for (i.e., to represent a return value that does not lie in the
 range of the return type). In this case, we don't have this problem as
 `NULL` serves this purpose.

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Ticket URL: <http://bind10.isc.org/ticket/2565#comment:4>
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