- lookup(): with a default value (const access)
For example,
Map<label> something;
value = something.lookup(key, -1);
being equivalent to the following:
Map<label> something;
value = -1; // bad value
if (something.found(key))
{
value = something[key];
}
except that lookup also makes it convenient to handle const references.
Eg,
const labelList& ids = someHash.lookup(key, labelList());
- For consistency, provide a two parameter HashTable '()' operator.
The lookup() method is, however, normally preferable when
const-only access is to be ensured.
- retain(): the counterpart to erase(), it only retains entries
corresponding to the listed keys.
For example,
HashTable<someType> largeCache;
wordHashSet preserve = ...;
largeCache.retain(preserve);
being roughly equivalent to the following two-stage process,
but with reduced overhead and typing, and fewer potential mistakes.
HashTable<someType> largeCache;
wordHashSet preserve = ...;
{
wordHashSet cull(largeCache.toc()); // all keys
cull.erase(preserve); // except those to preserve
largeCache.erase(cull); //
}
The HashSet &= operator and retain() are functionally equivalent,
but retain() also works with dissimilar value types.
- provide key_iterator/const_key_iterator for all hashes,
reuse directly for HashSet as iterator/const_iterator, respectively.
- additional keys() method for HashTable that returns a wrapped to
a pair of begin/end const_iterators with additional size/empty
information that allows these to be used directly by anything else
expecting things with begin/end/size. Unfortunately does not yet
work with std::distance().
Example,
for (auto& k : labelHashTable.keys())
{
...
}
- previously had a mismash of const/non-const attributes on iterators
that were confused with the attributes of the object being accessed.
- use the iterator keys() and object() methods consistently for all
internal access of the HashTable iterators. This makes the intention
clearer, the code easier to maintain, and protects against any
possible changes in the definition of the operators.
- 'operator*': The standard form expected by STL libraries.
However, for the std::map, this dereferences to a <key,value> pair,
whereas OpenFOAM dereferences simply to <value>.
- 'operator()': OpenFOAM treats this like the 'operator*'
- adjusted the values of end() and cend() to reinterpret from nullObject
instead of returning a static iteratorEnd() object.
This means that C++ templates can now correctly deduce and match
the return types from begin() and end() consistently.
So that range-based now works.
Eg,
HashTable<label> table1 = ...;
for (auto i : table1)
{
Info<< i << endl;
}
Since the 'operator*' returns hash table values, this prints all the
values in the table.
- This can be used as a convenient alternative to comparing against end().
Eg,
dictionaryConstructorTable::iterator cstrIter =
dictionaryConstructorTablePtr_->find(methodType);
if (cstrIter.found())
{
...
}
vs.
if (cstrIter != dictionaryConstructorTablePtr_->end())
{
...
}
- make table power-of-two, but since it seems to give 1-2% performance
improvement, maybe forget it too.
- remove two-argument form of hashing classes and do the modulus direclty
within HashTable instead. This simplifies things a fair bit.
- migrate Hash<void*> from db/dlLibrary to primitives/hashes/Hash
- much better performance on empty tables (4-6x speedup), neutral
performance change on filled tables. Since tableSize_ is non-zero when
nElmts_ is, there is no modulus zero problem.
- OSspecific: chmod() -> chMod(), even although it's not used anywhere
- ListOps get subset() and inplaceSubset() templated on BoolListType
- added UList<bool>::operator[](..) const specialization.
Returns false (actually pTraits<bool>::zero) for out-of-range elements.
This lets us use List<bool> with lazy evaluation and no noticeable
change in performance.
- use rcIndex() and fcIndex() wherever possible.
Could check if branching or modulus is faster for fcIndex().
- UList and FixedList get 'const T* cdata() const' and 'T* data()' members.
Similar to the STL front() and std::string::data() methods, they return a
pointer to the first element without needing to write '&myList[0]', recast
begin() or violate const-ness.
- The capitalization is consistent with most other template classes, but
more importantly frees up xfer() for use as method name without needing
special treatment to avoid ambiguities.
It seems reasonable to have different names for transfer(...) and xfer()
methods, since the transfer is occuring in different directions.
The xfer() method can thus replace the recently introduced zero-parameter
transfer() methods.
Other name candidates (eg, yield, release, etc.) were deemed too abstract.
StaticHashTable:
- erase(iterator&) now actually alters the iterator and iterator++() handles
it properly
- clear() also sets count to zero
- operator=(const StaticHashTable&) doesn't crash after a previous transfer
- operator(), operator==() and operator!=() added
HashTable:
- operator=(const HashTable&) gets tableSize if required, eg, after a
previous transfer)
HashSet / Map
- add xfer<...> constructor for underlying HashTable
