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<TITLE> [C++ Toolkit ANNOUNCE] Assignment and comparison of serializable classes (user-extendable)
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<H1>[C++ Toolkit ANNOUNCE] Assignment and comparison of serializable classes (user-extendable)</H1>
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<!--htdig_noindex-->
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<B>Denis Vakatov</B>
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<A HREF="mailto:cpp-announce%40ncbi.nlm.nih.gov?Subject=%5BC%2B%2B%20Toolkit%20ANNOUNCE%5D%20Assignment%20and%20comparison%20of%20serializable%20classes%20%28user-extendable%29&In-Reply-To="
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TITLE="[C++ Toolkit ANNOUNCE] Assignment and comparison of serializable classes (user-extendable)">vakatov at ncbi.nlm.nih.gov
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</A><BR>
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<I>Wed Jul 18 18:05:02 EDT 2001</I>
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<PRE>FYI,
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Added:
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+ template<class C> C& SerialAssign(C& dest, const C& src)
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+ template<class C> bool SerialEquals(const C& object1, const C& object2);
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+ class CSerialUserOp
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[ASSIGNMENT]
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Some time ago, we took steps to prohibit dangerous compiler-generated
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bit-wise copying and assignment for all of our generated serializable
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classes.
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However, as object copying still can be a necessity, so Aleksey
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Grichenko has implemented a special generic template function
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to copy one serializable object to another:
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template<class C> C& SerialAssign(C& dest, const C& src)
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(<A HREF="http://www.ncbi.nlm.nih.gov/IEB/ToolBox/CPP_DOC/lxr/ident?i=SerialAssign">http://www.ncbi.nlm.nih.gov/IEB/ToolBox/CPP_DOC/lxr/ident?i=SerialAssign</A>)
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For example:
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// For the particular class:
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CBioseq* BioseqClone(const CBioseq& bs)
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{
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CBioseq* new_bs = new CBioseq;
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SerialAssign<CBioseq>(*new_bs, bs);
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return new_bs;
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}
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// For any eligible class
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template<class C>
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C* SerialClone(const C& c)
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{
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C* new_c = new C;
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SerialAssign<C>(*new_c, c);
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return c;
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}
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ATTENTION! The destination object must be of exactly(!) the same type as
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the source one. Otherwise, an exception will be thrown in runtime.
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By default, only the serializable data of the object will be copied
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over by SerialAssign(). E.g., in case of "CBioseq", only members
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of its base class, "CBioseq_" would have been copied.
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If you want to provide for the copying of some (or all)
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non-serializable members as well, then you should inherit
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"CBioseq" from the special base class "CSerialUserOp" (in addition
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to "CBioseq_") and implement its virtual function:
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virtual void Assign(const CSerialUserOp& source);
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This function will be called right after all serializable members
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of "CBioseq" are copied over, and in CBioseq::Assign() you can
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copy non-serializable "CBioseq" data members manually:
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void CBioseq::Assign(const CSerialUserOp& source)
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{
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const CBioseq& src = dynamic_cast<const CBioseq&>(source);
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m_ParentEntry = src.m_ParentEntry;
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}
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[COMPARISON]
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The same technique should be used to provide for the serializable
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class comparison.
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The generic comparison function (template) is:
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template<class C> bool SerialEquals(const C& object1, const C& object2);
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(<A HREF="http://www.ncbi.nlm.nih.gov/IEB/ToolBox/CPP_DOC/lxr/ident?i=SerialEquals">http://www.ncbi.nlm.nih.gov/IEB/ToolBox/CPP_DOC/lxr/ident?i=SerialEquals</A>)
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and by default it compares only serializable data members.
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For example:
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// For the particular class:
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bool BioseqEquals(const CBioseq& bs1, const CBioseq& bs2)
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{
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return SerialEquals<CBioseq>(bs1, bs2);
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}
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To continue comparison in the case if all serializable data members
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are equal, you should inherit from "CSerialUserOp" and implement
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your own comparison method:
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virtual bool Equals(const CSerialUserOp& object) const;
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E.g. for "CBioseq":
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bool CBioseq::Equals(const CSerialUserOp& object) const
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{
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const CBioseq& obj = dynamic_cast<const CBioseq&>(object);
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return m_ParentEntry == obj.m_ParentEntry;
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}
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</PRE>
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