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LSST Data Management Base Package
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Public Member Functions | Related Symbols | List of all members
lsst::afw::typehandling::PolymorphicValue Class Referencefinal

Container that passes Storable objects by value while preserving type. More...

#include <PolymorphicValue.h>

Public Member Functions

 PolymorphicValue (Storable const &value)
 Create a new object containing a copy of a Storable.
 
 ~PolymorphicValue () noexcept
 
bool empty () const noexcept
 Check whether this object contains a Storable.
 
std::size_t hash_value () const
 Return a hash of this object (optional operation).
 
 PolymorphicValue (PolymorphicValue const &other)
 Try to copy a PolymorphicValue.
 
 PolymorphicValue (PolymorphicValue &&other) noexcept
 Try to copy a PolymorphicValue.
 
PolymorphicValueoperator= (PolymorphicValue const &other)
 Try to assign a PolymorphicValue.
 
PolymorphicValueoperator= (PolymorphicValue &&other) noexcept
 Try to assign a PolymorphicValue.
 
void swap (PolymorphicValue &other) noexcept
 Exchange the contents of this container and another.
 
 operator Storable & ()
 Return a reference to the internal Storable, if one exists.
 
 operator Storable const & () const
 Return a reference to the internal Storable, if one exists.
 
Storableget ()
 Return a reference to the internal Storable, if one exists.
 
Storable const & get () const
 Return a reference to the internal Storable, if one exists.
 
bool operator== (PolymorphicValue const &other) const noexcept
 Test whether the contained Storables are equal.
 
bool operator!= (PolymorphicValue const &other) const noexcept
 Test whether the contained Storables are equal.
 

Related Symbols

(Note that these are not member symbols.)

void swap (PolymorphicValue &lhs, PolymorphicValue &rhs) noexcept
 Swap specialization for PolymorphicValue.
 

Detailed Description

Container that passes Storable objects by value while preserving type.

This class is implicitly convertible to and from a reference to Storable, but behaves like a value: changing the internal Storable changes the object's state, and copying the object creates a new Storable.

Note
While a PolymorphicValue is always initialized with a Storable, it may become empty if it is the source of a move-construction or move-assignment. Conversion of an empty value to Storable& throws.

Definition at line 52 of file PolymorphicValue.h.

Constructor & Destructor Documentation

◆ PolymorphicValue() [1/3]

lsst::afw::typehandling::PolymorphicValue::PolymorphicValue ( Storable const & value)

Create a new object containing a copy of a Storable.

Parameters
valuethe value to copy into a PolymorphicValue

Definition at line 33 of file PolymorphicValue.cc.

33: _value(value.cloneStorable()) {}

◆ ~PolymorphicValue()

lsst::afw::typehandling::PolymorphicValue::~PolymorphicValue ( )
defaultnoexcept

◆ PolymorphicValue() [2/3]

lsst::afw::typehandling::PolymorphicValue::PolymorphicValue ( PolymorphicValue const & other)

Try to copy a PolymorphicValue.

Parameters
otherthe PolymorphicValue to copy.
Exceptions
UnsupportedOperationExceptionThrown if a copy is required and the object in other does not implement Storable::cloneStorable.

Definition at line 39 of file PolymorphicValue.cc.

40 : _value(other._value ? other._value->cloneStorable() : nullptr) {}

◆ PolymorphicValue() [3/3]

lsst::afw::typehandling::PolymorphicValue::PolymorphicValue ( PolymorphicValue && other)
defaultnoexcept

Try to copy a PolymorphicValue.

Parameters
otherthe PolymorphicValue to copy.
Exceptions
UnsupportedOperationExceptionThrown if a copy is required and the object in other does not implement Storable::cloneStorable.

Member Function Documentation

◆ empty()

bool lsst::afw::typehandling::PolymorphicValue::empty ( ) const
noexcept

Check whether this object contains a Storable.

Returns
true if this object has no Storable, false otherwise

Definition at line 62 of file PolymorphicValue.cc.

62{ return !_value; }

◆ get() [1/2]

Storable & lsst::afw::typehandling::PolymorphicValue::get ( )

Return a reference to the internal Storable, if one exists.

Returns
a reference to the internal object
Exceptions
pex::exceptions::LogicErrorThrown if this object is empty.

Definition at line 66 of file PolymorphicValue.cc.

66 {
67 // Both casts are safe; see Effective C++, Item 3
68 return const_cast<Storable&>(static_cast<PolymorphicValue const&>(*this).get());
69}
PolymorphicValue(Storable const &value)
Create a new object containing a copy of a Storable.

◆ get() [2/2]

Storable const & lsst::afw::typehandling::PolymorphicValue::get ( ) const

Return a reference to the internal Storable, if one exists.

Returns
a reference to the internal object
Exceptions
pex::exceptions::LogicErrorThrown if this object is empty.

Definition at line 70 of file PolymorphicValue.cc.

70 {
71 if (_value) {
72 return *_value;
73 } else {
74 throw LSST_EXCEPT(pex::exceptions::LogicError, "Dereferenced empty PolymorphicValue.");
75 }
76}
#define LSST_EXCEPT(type,...)
Create an exception with a given type.
Definition Exception.h:48

◆ hash_value()

std::size_t lsst::afw::typehandling::PolymorphicValue::hash_value ( ) const

Return a hash of this object (optional operation).

Exceptions
UnsupportedOperationExceptionThrown if the internal Storable is not hashable.

Definition at line 87 of file PolymorphicValue.cc.

87{ return std::hash<Storable>()(get()); }
Storable & get()
Return a reference to the internal Storable, if one exists.

◆ operator Storable &()

lsst::afw::typehandling::PolymorphicValue::operator Storable & ( )

Return a reference to the internal Storable, if one exists.

Returns
a reference to the internal object
Exceptions
pex::exceptions::LogicErrorThrown if this object is empty.

Definition at line 64 of file PolymorphicValue.cc.

64{ return get(); }

◆ operator Storable const &()

lsst::afw::typehandling::PolymorphicValue::operator Storable const & ( ) const

Return a reference to the internal Storable, if one exists.

Returns
a reference to the internal object
Exceptions
pex::exceptions::LogicErrorThrown if this object is empty.

Definition at line 65 of file PolymorphicValue.cc.

65{ return get(); }

◆ operator!=()

bool lsst::afw::typehandling::PolymorphicValue::operator!= ( PolymorphicValue const & other) const
inlinenoexcept

Test whether the contained Storables are equal.

Empty PolymorphicValues compare equal to each other and unequal to any non-empty PolymorphicValue.

Definition at line 130 of file PolymorphicValue.h.

130{ return !(*this == other); }

◆ operator=() [1/2]

PolymorphicValue & lsst::afw::typehandling::PolymorphicValue::operator= ( PolymorphicValue && other)
noexcept

Try to assign a PolymorphicValue.

To preserve the run-time type of the object in other, this method swaps (and possibly copies) the Storables instead of relying on the Storable's operator=.

Parameters
otherthe PolymorphicValue to overwrite this value with.
Exceptions
UnsupportedOperationExceptionThrown if a copy is required and the object in other does not implement Storable::cloneStorable.

Definition at line 51 of file PolymorphicValue.cc.

51 {
52 using std::swap;
53 swap(_value, other._value);
54 return *this;
55}
void swap(PolymorphicValue &other) noexcept
Exchange the contents of this container and another.
T swap(T... args)

◆ operator=() [2/2]

PolymorphicValue & lsst::afw::typehandling::PolymorphicValue::operator= ( PolymorphicValue const & other)

Try to assign a PolymorphicValue.

To preserve the run-time type of the object in other, this method swaps (and possibly copies) the Storables instead of relying on the Storable's operator=.

Parameters
otherthe PolymorphicValue to overwrite this value with.
Exceptions
UnsupportedOperationExceptionThrown if a copy is required and the object in other does not implement Storable::cloneStorable.

Definition at line 43 of file PolymorphicValue.cc.

43 {
44 if (other._value) {
45 _value = other._value->cloneStorable();
46 } else {
47 _value.reset();
48 }
49 return *this;
50}

◆ operator==()

bool lsst::afw::typehandling::PolymorphicValue::operator== ( PolymorphicValue const & other) const
noexcept

Test whether the contained Storables are equal.

Empty PolymorphicValues compare equal to each other and unequal to any non-empty PolymorphicValue.

Definition at line 78 of file PolymorphicValue.cc.

78 {
79 if (!empty() && !other.empty()) {
80 return get().equals(other.get());
81 } else {
82 // At least one pointer is null; pointer comparison has desired behavior
83 return _value == other._value;
84 }
85}
bool empty() const noexcept
Check whether this object contains a Storable.
virtual bool equals(Storable const &other) const noexcept
Compare this object to another Storable.
Definition Storable.cc:48

◆ swap()

void lsst::afw::typehandling::PolymorphicValue::swap ( PolymorphicValue & other)
noexcept

Exchange the contents of this container and another.

Definition at line 57 of file PolymorphicValue.cc.

57 {
58 using std::swap;
59 swap(_value, other._value);
60}

Friends And Related Symbol Documentation

◆ swap()

void swap ( PolymorphicValue & lhs,
PolymorphicValue & rhs )
related

Swap specialization for PolymorphicValue.

Definition at line 152 of file PolymorphicValue.h.

152{ lhs.swap(rhs); }

The documentation for this class was generated from the following files: