John Leveon asked me how you would specify that one kind of inset is
searchable but not spell-checkable, and that another kind of inset is
spell-checkable and not searchable. Here is a complete self-contained
example.
class InsetVisitor;
class Inset {
// blah blah
virtual void Accept(InsetVisitor&) = 0;
};
class InsetSpellCheckable : public Inset {
// blah blah
virtual void Accept(InsetVisitor& iv ) { iv.VisitInsetA(*this); }
};
class InsetSearchable : public Inset {
// blah blah
virtual void Accept(InsetVisitor& iv ) { iv.VisitInsetB(*this); }
};
class InsetVisitor {
// blah blah
virtual void VisitInsetSpellCheckable( InsetSpellCheckable& ) = 0;
virtual void VisitInsetSearchable( InsetSearchable& ) = 0;
};
// Once-off infrastructure
class InsetVisitorNOP : public InsetVisitor {
virtual void VisitInsetSpellCheckable( InsetSpellCheckable& ) {}
virtual void VisitInsetSearchable( InsetSearchable& ) {}
};
class SpellCheckInsetVisitor : public InsetVisitorNOP {
// blah blah
public:
virtual void VisitInsetSpellCheckable( InsetSpellCheckable& i ) {
// Carry out spellcheck on contents of InsetSpellcheckable
}
};
class SearchableInsetVisitor : public InsetVisitorNOP {
// blah blah
public:
virtual void VisitInsetSearchable( InsetSearchable& i ) {
// Carry out search on contents of InsetSearchable
}
};
Note that only one set of Accepts methods is necessary in the Insets to
support both (and any other) kinds of visitors.
Furthermore, you may define a modular exporter:
// Export to text file
class WriteAsTextInsetVisitor
: public InsetVisitor // Compiler will give errors if new class is
added that we didn't visit.
{
public:
virtual void VisitInsetSearchable( InsetSearchable& i ) {
// Write out an InsetSearchable as text format, including any
sub-insets...
}
virtual void VisitInsetSpellCheckable( InsetSpellCheckable& i ) {
// Write out an InsetSpellCheckable as text format, including
any sub-insets...
}
};
Note that this visitor could be placed into a dynamic link library if
required, or conditionally compiled, or whatever... it has completely
removed the export code from all of the insets. It could be a new
feature you are adding for testing (without touching any existing inset
code).
Ben.
