Re: Deriving from concrete types

From:

brangdon@cix.co.uk (Dave Harris)

Newsgroups:

comp.lang.c++.moderated

Date:

6 Jul 2006 18:17:45 -0400

Message-ID:

<memo.20060706201055.2744A@brangdon.cix.compulink.co.uk>

SeeWebsiteForEmail@erdani.org (Andrei Alexandrescu (See Website For
Email)) wrote (abridged):

struct KeywordData : public std::vector<Entry> { std::string keyword;
};
std::vector<KeywordData> tableData;

Congratulations, you've just invented std::pair.

I think "first" is rather a poor name for the member, so I'd prefer the
Alan McKenney's initial solution:

   struct KeywordData { std::vector<Entry> data; std::string keyword; };

(Although "data" is a poor name too; if they are entries I'd call them
"entries".)

Either way it changes the interface to the object. Code that looked like:

    int value = keywordData.front().value;

won't compile any more. Instead we need:

    int value = keywordData.data.front().value;

which he rejected. He didn't say why, but long chains of dots like that
kinda go against the "Law of Demeter" and it makes me a bit uncomfortable.

-- Dave Harris, Nottingham, UK.

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