- offers similarity with bitSet

STYLE: remove remnant parent::operator= from HashSet

STYLE: code formatting in HashTables

The fakeError function object emits FatalError at different stages (or
does nothing), which is useful for testing purposes (issue #1779).

Can request errors from constructor, execute and write methods.

- previously setting FOAM_ABORT would preempt checks for throwing
  exceptions.

  Now check for throwing first, to allow try/catch code to do its job.
  However, ignore exception throwing for abort(). These are used
  infrequently in the code, but indicate that recovery is deemed
  impossible.

STYLE: use unique_ptr for internal stream buffer management

The function evaluate was returning true every outer loop, triggering
the re-calculation of ddt0 in every outer loop.

The evaluation of the term ddt0 should be performed once per time step.
The corrected function updates the timeIndex of ddt0 to avoid the
re-evaluation of this term in the outer loops.

- improves flexibility. Can tag a tmp as allowing non-const access to
  the reference and skip additional const_cast in following code. For
  example,

      tmp<volScalarField> tfld(nullptr);
      auto* ptr = getObjectPtr<volScalarField>("field");
      if (ptr)
      {
          tfld.ref(*ptr);
      }
      else
      {
          tfld.reset(volScalarField::New(...));
      }
      auto& fld = tfld.ref();

ENH: renamed tmpNrc to refPtr

- the name 'refPtr' (reference|pointer) should be easier to remember
  than tmpNrc (tmp, but non-ref-counted).

- provide tmpNrc typedef and header for code compatibility

NOTE

- in some places refPtr and tmp can be used instead of a
  std::reference_wrapper for handling external references.

  Unlike std::reference_wrapper, it can be default constructed
  (holding nothing), whereas reference_wrapper may need a dummy
  reference. However, the lifetime extension of references _may_ be
  better with reference_wrapper.

autoPtr/tmp cleanup

See merge request !378

- Cannot call ptr_->clone() with a null pointer!

- autoPtr: less clutter using plain tests with the bool operator

    (!ptr)  vs  (ptr.empty())
    (ptr)   vs  (!ptr.empty())

- tmp: was entirely unused.

- previously this was marked as '= delete' for consistency with
  assignment from an empty pointer being a runtime error.
  However, these can be considered semantically different and it makes
  sense to permit this as equivalent to reset(nullptr).

  This change does not break existing code since the operator was
  previously unavailable (deleted).

STYLE: refactor tmp operator=(T*)

- delegate to reset() after initial checks

- Previously considered to be valid() if it was any reference
  (null or non-null) or a non-null pointer.

  This appears to be a holdover from old code (pre-2015) where
  reinterpret_cast<..>(0) was used instead of the NullObject.

  A reference via a null pointer isn't really possible anywhere. Even
  for things like labelList::null(), they now use the NullObject,
  which has a non-zero memory location.

- now simply check for a non-zero memory address. Regardless of
  pointer or referenced object.

- combine reset() methods by adding a default parameter

- improve top-level visibility of empty/valid/get methods for symmetry
  symmetry with autoPtr, future adjustment

- cleaner code, more similarity with unique_ptr

  Now
      if (ptr)
      if (!ptr)

  instead
      if (ptr.valid())
      if (!ptr.valid())

- with '&&' conditions, often better to check for non-null autoPtr
  first (it is cheap)

- check as bool instead of valid() method for cleaner code, especially
  when the wrapped item itself has a valid/empty or good.
  Also when handling multiple checks.

  Now
      if (ptr && ptr->valid())
      if (ptr1 || ptr2)

  instead
      if (ptr.valid() && ptr->valid())
      if (ptr1.valid() || ptr2.valid())

- less clutter using plain tests with the bool operator:

      (!ptr)  vs  (ptr.empty())
      (ptr)   vs  (!ptr.empty())

- same as FixedList<bool,3> for I/O

- since only pointers are stored, autoPtr is better fit than tmp

Feature dynamic library - issue #1737

See merge request !375

- This reflects the pre-existing coding situation where const_cast was
  used throughout to effect the same.

STYLE: fix private/protected access

- CodedField, codedMixedFvPatchField

- libs() singleton method for global library handling

- explicit handling of empty filename for dlLibraryTable open/close.
  Largely worked before, but now be more explicit about its behaviour.

- add (key, dict) constructor and open() methods.
  More similarity to dimensionedType, Enum etc, and there is no
  ambiguity with the templated open().

- construct or open from initializer_list of names

- optional verbosity when opening with auxiliary table,
  avoid duplicate messages or spurious messages for these.

- basename and fullname methods (migrated from dynamicCode).

- centralise low-level load/unload hooks

- adjust close to also dlclose() aliased library names.

This is for a very specific use case where the faceZones are
imprinted after meshing the normal geometry. This sometimes
splits off badly connected bits of the mesh. One way to remove
these is to use e.g. subsetMesh. This embeds the
same functionality inside snappyHexMesh.

- replace `%namespace` directive with simpler `%static` directive.

  We always encapsulate Lemon parser routines in an anonymous
  namespace, so a simpler static linkage directive suffices.

  This reduces the size of the Lemon patch (program and template).

- makes it easier to distinguish between pointers referring to pool
  data versus pointers actually holding storage, avoids
  manual demand-driven deletion and autoPtr.

ENH: simplify/improve Pstream profiling

- times now double (not scalar) for consistency with what cpuTime
  delivers

- use bool to track suspend state