lsst::afw::table::Key< T > Class Template Reference

A class used as a handle to a particular field in a table. More...

#include <fwd.h>

Public Member Functions
template<typename OtherT >
bool	operator== (Key< OtherT > const &other) const noexcept
	Equality comparison. More...
template<typename OtherT >
bool	operator!= (Key< OtherT > const &other) const noexcept
bool	operator== (Key const &other) const noexcept
bool	operator!= (Key const &other) const noexcept
std::size_t	hash_value () const noexcept
	Return a hash of this object. More...
int	getOffset () const noexcept
	Return the offset (in bytes) of this field within a record. More...
bool	isValid () const noexcept
	Return true if the key was initialized to valid offset. More...
	Key () noexcept
	Default construct a field. More...
	Key (Key const &) noexcept=default
	Key (Key &&) noexcept=default
Key &	operator= (Key const &) noexcept=default
Key &	operator= (Key &&) noexcept=default
	~Key () noexcept=default

Friends
class	detail::Access
class	BaseRecord
std::ostream &	operator<< (std::ostream &os, Key< T > const &key)
	Stringification. More...

Detailed Description

template<typename T>
class lsst::afw::table::Key< T >

A class used as a handle to a particular field in a table.

All access to table data ultimately goes through Key objects, which know (via an internal offset) how to address and cast the internal data buffer of a record or table.

Keys can be obtained from a Schema by name:

schema.find("myfield").key

and are also returned when a new field is added. Compound and array keys also provide accessors to retrieve scalar keys to their elements (see the documentation for the KeyBase specializations), even though these element keys do not correspond to a field that exists in any Schema. For example:

Schema schema;
Key< Array<float> > arrayKey = schema.addField< Array<float> >("array", "docs for array", 5);
Key< Point<int> > pointKey = schema.addField< Point<int> >("point", "docs for point");
Key<float> elementKey = arrayKey[3];
Key<int> xKey = pointKey.getX();
std::shared_ptr<BaseTable> table = BaseTable::make(schema);
std::shared_ptr<BaseRecord> record = table.makeRecord();
assert(&record[arrayKey][3] == &record[elementKey3]);
assert(record.get(pointKey).getX() == record[xKey]);

Key inherits from FieldBase to allow a key for a dynamically-sized field to know its size without needing to specialize Key itself or hold a full Field object.

Definition at line 45 of file fwd.h.

Constructor & Destructor Documentation

Key() [1/3]

template<typename T >

lsst::afw::table::Key< T >::Key ( )

inlinenoexcept

Default construct a field.

The new field will be invalid until a valid Key is assigned to it.

Definition at line 104 of file Key.h.

: FieldBase<T>(FieldBase<T>::makeDefault()), _offset(-1) {}

Key() [2/3]

template<typename T >

lsst::afw::table::Key< T >::Key ( Key< T > const &  )

defaultnoexcept

Key() [3/3]

template<typename T >

lsst::afw::table::Key< T >::Key ( Key< T > &&  )

defaultnoexcept

~Key()

template<typename T >

lsst::afw::table::Key< T >::~Key ( )

defaultnoexcept

Member Function Documentation

getOffset()

template<typename T >

int lsst::afw::table::Key< T >::getOffset ( ) const

inlinenoexcept

Return the offset (in bytes) of this field within a record.

Definition at line 87 of file Key.h.

{ return _offset; }

hash_value()

template<typename T >

std::size_t lsst::afw::table::Key< T >::hash_value ( ) const

inlinenoexcept

Return a hash of this object.

Definition at line 81 of file Key.h.

                                          {
        // Completely arbitrary seed
        return utils::hashCombine(17, _offset, this->getElementCount());
    }

isValid()

template<typename T >

bool lsst::afw::table::Key< T >::isValid ( ) const

inlinenoexcept

Return true if the key was initialized to valid offset.

This does not guarantee that a key is valid with any particular schema, or even that any schemas still exist in which this key is valid.

A key that is default constructed will always be invalid.

Definition at line 97 of file Key.h.

{ return _offset >= 0; }

operator!=() [1/2]

template<typename T >

bool lsst::afw::table::Key< T >::operator!= ( Key< T > const &  other ) const

inlinenoexcept

Definition at line 77 of file Key.h.

{ return !this->operator==(other); }

operator!=() [2/2]

template<typename T >

template<typename OtherT >

bool lsst::afw::table::Key< T >::operator!= ( Key< OtherT > const &  other ) const

inlinenoexcept

Definition at line 70 of file Key.h.

                                                             {
        return true;
    }

operator=() [1/2]

template<typename T >

Key& lsst::afw::table::Key< T >::operator= ( Key< T > &&  )

defaultnoexcept

operator=() [2/2]

template<typename T >

Key& lsst::afw::table::Key< T >::operator= ( Key< T > const &  )

defaultnoexcept

operator==() [1/2]

template<typename T >

bool lsst::afw::table::Key< T >::operator== ( Key< T > const &  other ) const

inlinenoexcept

Definition at line 74 of file Key.h.

                                                     {
        return _offset == other._offset && this->getElementCount() == other.getElementCount();
    }

operator==() [2/2]

template<typename T >

template<typename OtherT >

bool lsst::afw::table::Key< T >::operator== ( Key< OtherT > const &  other ) const

inlinenoexcept

Equality comparison.

Two keys with different types are never equal. Keys with the same type are equal if they point to the same location in a table, regardless of what Schema they were constructed from (for instance, if a field has a different name in one Schema than another, but is otherwise the same, the two keys will be equal).

Definition at line 66 of file Key.h.

                                                             {
        return false;
    }

Friends And Related Function Documentation

BaseRecord

template<typename T >

friend class BaseRecord

friend

Definition at line 120 of file Key.h.

detail::Access

template<typename T >

friend class detail::Access

friend

Definition at line 119 of file Key.h.

operator<<

template<typename T >

std::ostream& operator<< ( std::ostream &  os, Key< T > const &  key  )

friend

Stringification.

Definition at line 113 of file Key.h.

                                                                            {
        return os << "Key<" << Key<T>::getTypeString() << ">(offset=" << key.getOffset()
                  << ", nElements=" << key.getElementCount() << ")";
    }

---

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

• /j/snowflake/release/lsstsw/stack/cb4e2dc/Linux64/afw/20.0.0-16-gfab17e72e+fdf35455f6/include/lsst/afw/table/fwd.h
• /j/snowflake/release/lsstsw/stack/cb4e2dc/Linux64/afw/20.0.0-16-gfab17e72e+fdf35455f6/include/lsst/afw/table/Key.h