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DesignPattern::Creation🔗

This pattern can be used if you write an abstraction where you have to throw an exception in the constructor when you for instance would like to manage a resource and the constructor was unable to acquire that resource. In this case you inherit from [Creation]() and your class has three more static factory methods - create, placementCreate and verify. create forwards all arguments to the underlying class constructor and if the construction was successful an expected containing the type is returned, otherwise an error value which describes the error. Additionally, this class is providing two protected member variables m_isInitialized and m_errorValue. The user always has to set m_isInitialized to true when the object construction was successful otherwise one sets it to false and write the corresponding error cause in the provided m_errorValue variable which is then returned to the user. More...

#include <iceoryx_hoofs/design_pattern/creation.hpp>

Public Types🔗

Name
using Creation< DerivedClass, ErrorType > CreationPattern_t
using iox::cxx::expected< DerivedClass, ErrorType > result_t
using ErrorType errorType_t

Public Functions🔗

Name
template <typename... Targs>
result_t		 create(Targs &&... args)
factory method which guarantees that either a working object is produced or an error value describing the error during construction
result_t verify(DerivedClass && newObject)
verifies if a class was created successfully
template <typename... Targs>
iox::cxx::expected< ErrorType >		 placementCreate(void *const memory, Targs &&... args)
factory method which guarantees that either a working object is produced or an error value describing the error during construction
Creation() =default
Creation(Creation && rhs)
Creation & operator=(Creation && rhs)
Creation(const Creation & rhs) =default
Creation & operator=(const Creation & rhs) =default
bool isInitialized() const
returns true if the object was constructed successfully, otherwise false

Protected Attributes🔗

Name
bool m_isInitialized
ErrorType m_errorValue

Detailed Description🔗

template <typename DerivedClass ,
typename ErrorType >
class DesignPattern::Creation;

This pattern can be used if you write an abstraction where you have to throw an exception in the constructor when you for instance would like to manage a resource and the constructor was unable to acquire that resource. In this case you inherit from [Creation]() and your class has three more static factory methods - create, placementCreate and verify. create forwards all arguments to the underlying class constructor and if the construction was successful an expected containing the type is returned, otherwise an error value which describes the error. Additionally, this class is providing two protected member variables m_isInitialized and m_errorValue. The user always has to set m_isInitialized to true when the object construction was successful otherwise one sets it to false and write the corresponding error cause in the provided m_errorValue variable which is then returned to the user.

Template Parameters:

  • DerivedClass the class which inherits from the creation pattern
  • ErrorType the error type which is going to be used when an error occurs 
enum class MyResourceAbstractionError {
  ResourceNotAvailable,
  BlaBlubError
};
class MyResourceAbstraction : public Creation<MyResourceAbstraction, MyResourceAbstractionError> {
  public:
    // some public methods
    MyResourceAbstraction & operator=(MyResourceAbstraction && rhs) noexcept {
      if ( this != &rhs ) {
        // always call the creation move assignment operator when you have a user defined
        // move operation
        CreationPattern_t::operator=(std::move(rhs));

        // user move code
      }
      return *this;
    }

    // the creation pattern is the only one which should be allowed to construct
    // the class, therefore it has to be friend of that class
    friend class Creation<MyResourceAbstraction, MyResourceAbstractionError>;
  private:
    MyResourceAbstraction(int a) {
      if ( a > 0) {
        // we are able to initialize the class an set m_isInitialized to true
        m_isInitialized = true;
      } else {
        // we are unable to construct the class therefore we have to set
        // m_isInitialized to false and store the error code in the
        // provided m_errorValue member
        m_errorValue = MyResourceAbstractionError::ResourceNotAvailable;
        m_isInitialized = false;
      }
    }
}

// if the system resource is movable
auto resource = MyResourceAbstraction::Create(123);
if ( resource.has_error() && resource.get_error() == MyResourceAbstractionError::ResourceNotAvailable )
  // perform error handling
else
  // perform some work

// if the system resource is not movable
MyResourceAbstraction * resource = malloc(sizeof(MyResourceAbstraction));
auto result = MyResourceAbstraction::placementCreate(resource, 123);
if ( result.has_error() )
  // perform error handling
else
  resource->DoStuff();

delete resource;

Public Types Documentation🔗

using CreationPattern_t🔗

using DesignPattern::Creation< DerivedClass, ErrorType >::CreationPattern_t =  Creation<DerivedClass, ErrorType>;

using result_t🔗

using DesignPattern::Creation< DerivedClass, ErrorType >::result_t =  iox::cxx::expected<DerivedClass, ErrorType>;

using errorType_t🔗

using DesignPattern::Creation< DerivedClass, ErrorType >::errorType_t =  ErrorType;

Public Functions Documentation🔗

function create🔗

template <typename... Targs>
static result_t create(
    Targs &&... args
)

factory method which guarantees that either a working object is produced or an error value describing the error during construction

Parameters:

  • args the argument values which will be forwarded to the ctor

Template Parameters:

  • Targs the argument types which will be forwarded to the ctor

Return: returns an expected which either contains the object in a valid constructed state or an error value stating why the construction failed.

function verify🔗

static result_t verify(
    DerivedClass && newObject
)

verifies if a class was created successfully

Parameters:

  • newObject rvalue of the object which should be verified

Return: returns an expected which either contains the object in a valid constructed state or an error value stating why it was in an invalid state.

function placementCreate🔗

template <typename... Targs>
static iox::cxx::expected< ErrorType > placementCreate(
    void *const memory,
    Targs &&... args
)

factory method which guarantees that either a working object is produced or an error value describing the error during construction

Parameters:

  • memory a piece of memory where the object is created into with placement new
  • args the argument values which will be forwarded to the ctor

Template Parameters:

  • Targs the argument types which will be forwarded to the ctor

Return: returns an expected which either contains the object in a valid constructed state or an error value stating why the construction failed.

function Creation🔗

Creation() =default

function Creation🔗

Creation(
    Creation && rhs
)

function operator=🔗

Creation & operator=(
    Creation && rhs
)

function Creation🔗

Creation(
    const Creation & rhs
) =default

function operator=🔗

Creation & operator=(
    const Creation & rhs
) =default

function isInitialized🔗

bool isInitialized() const

returns true if the object was constructed successfully, otherwise false

Protected Attributes Documentation🔗

variable m_isInitialized🔗

bool m_isInitialized {false};

variable m_errorValue🔗

ErrorType m_errorValue;

Updated on 31 May 2022 at 11:34:55 CEST