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BerkeleyDB for D programming language

This package provides 2 version of interface to BerkeleyDB library for D:

- The first version repeats C-interface. This interfaces generates from 
  BerkeleyDB headers and therefore easy maybe regenerated for new version
  BerkeleyDB. Also when D language changes there will small changes to
  fix this interface generation.
  Already generated file for BerkeleyDB 6.1.26.NC maybe found at 
  "berkeleydb/c.d" file.
  Generator - AWK-program bdb2d.awk.
  To regenerate interface enough to change in the script path
  to Berkeleydb sources from "~/Programs/db-6.1.26.NC" to your
  path. After that run "./"

- The second version tries to be more like D-interface. 
  Below there is description of interface base idea.

Interface consists of:
- 10 classes which repears according BDB structures: 
  Dbc, DbChannel, Db, DbEnv, DbLogc, DbMpoolfile, DbSequence, DbSite,
  DbStream, DbTxn.
- 7 classes of exceptions, 5 of which repeats exceptions from C++ BDB interface:
  DbException, DbWrongUsingException, DbDeadlockException
  DbLockNotGrantedException, DbMemoryException, DbRepHandleDeadException,
- structure Dbt and yet 3 attendant structures:
  UserMemDbt, BulkDbt, RecnoBulkDbt

Interfaces of classes repeats BDB interfaces but follows then next ideas:
1) Methods like db_create/db_env_create in this library
   replaced with constructors of according class.
2) As for the rest names of methods fully equals.
3) Instead of"const char*" always used "string"
4) Instead of other arrays like DB_LOCKREQ* argument in the DB_ENV->lock_vec
   function with reference of length in the disctinct argument used D arrays
   like DbLockreq[] in the DbEnv.lock_vec which consists of
   pointer and length in the one argument
5) Instead of code errors used exceptions. The most functions turns to
   void return. The exceptions are functions like db.get, which may return
   not error codes (DB_KEYEMPTY, DB_NOTFOUND etc.). Full list of such functions maybe
   found in the implementation of "DbRetCodeToException" function
   (berkeleydb/dbexception.d file)
6) Of course the first argument - pointer to the class is hidden
   (for example DB_ENV *dbenv in the example of 7-th item)
7) When function returns the single value, pointer argument turns
   to return value. For example the function
   int DB_ENV->get_open_flags(DB_ENV *dbenv, u_int32_t *flagsp);
   turned to
   uint32_t DbEnv.get_open_flags()
   I.e. function now returns flags instead of error code
8) Functions which gets or returns 2 arguments gbytes, bytes
   have 2 interfaces: one like C-version with 2 arguments and
   the secon with one 64-bit bytes argument. For example:
   void DbEnv.set_memory_max(uint32_t gbytes, uint32_t bytes)
   void DbEnv.set_memory_max(uint64_t bytes)
   void DbEnv.get_memory_max(ref uint32_t gbytes, ref uint32_t bytes)
   uint64_t DbEnv.get_memory_max()
9) Callbacks also uses D-arguments, for example "DbEnv" instead of "DB_ENV*",
   string instead of char *, etc.
10) The last flags argument maybe skipped if it equals zero.

Dbt structure with hidden methods declared as:

struct Dbt
	DBT dbt;
	alias dbt this;

This means that you can refer to Dbt type fields also as to DBT. 
Besides this you can cast (DBT*) to (Dbt*) and vice-versa. 
And even Dbt[] array maybe easily converted to C-style array
with cast(DBT*)Dbt.ptr. 
But also Dbt can such:

    string hello = "Hello, world!";

	Dbt dbt = hello; // and dbt.size filled with one assignment.
	assert(dbt.size == hello.length);

	assert(!string() == "Hello, world!"); //back conversion 
	assert(!string() is "Hello, world!");

	struct S
		int a;
		byte b;
	S s;
	s.a = 5000;
	s.b = 22;

	Dbt dbt_struct;
    dbt_struct = s; //again & dbt_struct.size by one instruction
	assert( dbt_struct.size == s.sizeof );
	assert(!S() == s ); //back

	S *ps =!(S*)(); //You may also convert to pointer
	assert( *ps == s );
	assert( ps is &s );

Also you can use UserMemDbt, but it gets size of user-memory buffer
in the constructor. As distinct from Dbt when assignment value 
to UserMemDbt it will copied to buffer, not just referenced to
UserMemDbt* pointer maybe casted to (Dbt*) and vice versa.

BulkDbt/RecnoBulkDbt maybe used for bulk insert/get operations. 
Both maybe casted to (Dbt*) but not vice versa. For back conversion
use BulkDbt(ref Dbt dbt) and RecnoBulkDbt(ref Dbt dbt) constructors.
For examples see unittests in the berkeleydb/dbt.d

For example of using library see transactions_test directory

Bugs of library:
1) Interface sometimes maybe not consistent. For example
   sometimes translate pointer to ref-argument, and sometimes leave it
   as pointer.
2) Some functions like DbEnv.memp_stat seems may be reasons of
   memory leaks.
3) If for Db close called explicitly, but for cursor Dbc not called before,
   it will called implicitly in the destructor and will cause of an error. 
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