Sheaf

Overview

The sheaf is the datastructure returned by the "SELECT (ALL|FOCUS) OBJECTS" query. See the MQL User's Guide Chapter 4 for a description of the sheaf.

Briefly, a sheaf is a list of straws. A straw is a list of matched_objects. A matched_object may have an inner sheaf, which makes the datastructure recursive.

A matched_object corresponds to an object_block(_first) or (opt_)gap_block in a topographic MQL query. A straw corresponds to a block_string. A sheaf corresponds to a blocks.

Java-style iterators are provided.

C++ interface

#include <emdros/mql_sheaf.h>


typedef enum { 
  kMOKNIL_mo,   // Used only while building sheaf, never in finished sheaf
  kMOKEMPTY_mo, // Used only while building sheaf, never in finished sheaf
  kMOKID_D,     // Match of object_block(_first)
  kMOKID_M      // Match of (opt_)gap_block
} eMOKind;

class CMatched_object {
public:  
  CMatched_object(const CMatched_object{PREAMP} other);
  ~CMatched_object();
  const CSet_of_monad_ms{PREAMP} get_monads(void) const;
  id_d_t get_id_d(void) const;
  const CSheaf* get_sheaf(void) const;
  bool sheaf_is_empty(void) const;
  eMOKind get_kind(void) const;
  bool get_focus(void) const;
  CMatched_object{PREAMP} operator=(const CMatched_object{PREAMP} other); // Not SWIG-wrapped
  short int get_object_type_index(void) const { return m_object_type_index; };
  void put_Console(CEMdFOutput *pOut) const;
  void put_XML(CEMdFOutput* pOut) const;
};

class StrawConstIterator {
public:
  StrawConstIterator(const CStraw *pMotherStraw);
  StrawConstIterator();
  StrawConstIterator(const StrawConstIterator{PREAMP} other);
  ~StrawConstIterator();
  bool hasNext() const; // Is the iterator == end iterator?  Doesn't alter iterator
  const CMatched_object* next(); // Gets current and advances iterator afterwards
  const CMatched_object* previous(); // Regresses iterator and then gets current
  const CMatched_object* current(); // Gets current without altering iterator
};

class CStraw {
private:
  friend class StrawConstIterator;
  monad_m m_last;
  MOList m_list;
public:
  ~CStraw();
  CStraw(const CStraw{PREAMP} other);
  StrawConstIterator const_iterator() const;
  CStraw{PREAMP} operator=(const CStraw{PREAMP} other); // Not SWIG-wrapped
  monad_m get_last(void) const { return m_last; };
  void put_Console(CEMdFOutput *pOut) const;
  void put_XML(CEMdFOutput* pOut) const;
};

class SheafIterator {
public:
  SheafIterator(CList_of_straws *pMotherList);
  SheafIterator();
  SheafIterator(const SheafIterator{PREAMP} other);
  ~SheafIterator();
  bool hasNext() const; // Is the iterator == end iterator?  Doesn't alter iterator
  CStraw* next(); // Gets current and advances iterator afterwards
  CStraw* previous(); // Regresses iterator and then gets current
  CStraw* current(); // Gets current without altering iterator
};



class SheafConstIterator {
public:
  SheafConstIterator(const CList_of_straws *pMotherList);
  SheafConstIterator();
  SheafConstIterator(const SheafConstIterator{PREAMP} other);
  ~SheafConstIterator();
  bool hasNext() const; // Is the iterator == end iterator?  Doesn't alter iterator
  const CStraw* next(); // Gets current and advances iterator afterwards
  const CStraw* previous(); // Regresses iterator and then gets current
  const CStraw* current(); // Gets current without altering iterator
};



class CList_of_straws {
public:
  ~CList_of_straws();
  CList_of_straws(const CList_of_straws{PREAMP} other);
  SheafIterator iterator();
  SheafConstIterator const_iterator() const;
  bool is_empty() const;
  void put_Console(CEMdFOutput *pOut) const;
  void put_XML(CEMdFOutput* pOut) const;
};

class CSheaf {
public:
  CSheaf(const CSheaf{PREAMP} other);
  ~CSheaf();
  bool is_fail(void) const;
  SheafIterator iterator();
  SheafConstIterator const_iterator() const;
  const CList_of_straws* get_plist(void) const { return m_plist; };
  CSheaf{PREAMP} operator=(const CSheaf{PREAMP} other); // Not SWIG-wrapped
  void put_Console(CEMdFOutput *pOut) const;
  void put_XML(CEMdFOutput* pOut) const;
  // Print sheaf's contribution to DTD
  static void print_DTD(CEMdFOutput* pOut);
};

Example

The iterators are used like this:

  CSheaf *pSheaf; // Assumed to be initialized from somewhere
  SheafConstIterator sci = pSheaf->const_iterator();
  while (sci.hasNext()) {
    const CStraw *pStraw = sci.current();
   
    // Process pStraw ...

    sci.next();
  }

  // Or like this:
  SheafIterator si = pSheaf->iterator();
  while (si.hasNext()) {
    CStraw *pStraw = si.next();
   
    // Process pStraw ...

    // Note how there is no si.next() again, since next() 
    // first gets current element and then advances iterator.

    // NOTE: This is also possible with the const iterators.

  }