Copy assignment of Partition objects is now only performed in a few
places in the Operation and OperationResizeMove classes when updating
the displayed PartitionVector. (From Refresh_Visual() when each
operation is visually applied to the display_partitions vector; the
new_partition from the operation is copy assigned over the top of the
relevant existing partition in the display_partitions vector).
In general polymorphic copy assignment is complicated [1], and is now
unnecessary given the above limited use. All that is needed is a way to
polymorphically replace one Partition object with another in a
PartitionVector.
First, prevent further use of Partition object copy assignment by
providing a private declaration and no implementation, so the compiler
enforces this. Second implement and use PartitionVector method
replace_at() which replaces a pointer to one Partition object with
another at the specified index in the PartitionVector.
[1] The Assignment Operator Revisited
[Section:] Virtual assignment
http://icu-project.org/docs/papers/cpp_report/the_assignment_operator_revisited.html
Bug 759726 - Implement Partition object polymorphism
Remove PartitionVector push_back() and insert() methods which copy
construct Partitions objects into the vector. All the code has already
been changed to dynamically allocate Partition objects and use the
adoption variants of these methods named, push_back_adopt() and
insert_adopt(). Remove the no longer used methods.
Bug 759726 - Implement Partition object polymorphism
The current code uses push_back() and insert() to copy Partition objects
into the vector of pointers. This has a few issues:
1) Unnecessary copying of Partition objects;
2) Hides the nature of the PartitionVector class as a manager of
pointers to Partition objects by providing copy semantics to add
items. It is generally better to be explicit;
3) C++ doesn't provide polymorphic copy construction directly, but this
is easily worked around by following the Virtual Constructor idiom
[1], which would allow PartitionLUKS derived class objects to be
copied into the vector.
Add push_back_adopt() and insert_adopt() methods which add a pointer to
a Partition object into the PartitionVector adopting ownership.
[1] Wikibooks: More C++ Idioms / Virtual Constructor
https://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Virtual_Constructor
Bug 759726 - Implement Partition object polymorphism
The PartitionVector class is now internally using pointers to Partition
objects and taking on management of their lifetimes. It therefore has
to implement the Big 3: destructor, copy constructor and copy assignment
operator [1][2]. This is because the implicitly-defined copy
constructor and assignment operator perform memberwise "shallow copying"
and the destructor does nothing. This not correct for classes which
contain non-class types such as raw pointers.
The semantics of the interface still copies each Partition object into
the PartitionVector when they are added with push_back() and insert().
Note that a PartitionVector object is explicitly copy assigned in
Win_GParted::Refresh_Visual(). They are also implicitly copied when
(1) the implementing vector is resized larger to allow it to hold more
pointers to Partition objects than it previously had capacity for; and
(2) a Partition object is copied including the logicals PartitionVector
member.
[1] The rule of three/five/zero
http://en.cppreference.com/w/cpp/language/rule_of_three
[2] Rule of Three
https://en.wikipedia.org/wiki/Rule_of_three_%28C%2B%2B_programming%29
Bug 759726 - Implement Partition object polymorphism
Just creates PartitionVector class and includes it in partition.h so
that it is built and validated by the compiler. Not used anywhere yet.
Implementation strategy is to create a PartitionLUKS class derived from
the Partition class. This implies polymorphism of Partition objects,
which in C++ requires using pointers and references to objects, and not
using objects directly. (See C++ object slicing). Later this
PartitionVector class will be modified to use pointers to Partition
objects and act as the owner of the pointed to Partition objects.
Bug 759726 - Implement Partition object polymorphism
Mike Fleetwood