Qore::HashReverseIterator Class Reference

This class an iterator class for hashes. More...

Inheritance diagram for Qore::HashReverseIterator:

Public Member Methods
	constructor (hash< auto > h)
	Creates the hash iterator object. More...
	constructor ()
	Creates an empty iterator object. More...
	copy ()
	Creates a copy of the HashReverseIterator object, iterating the same object as the original and in the same position. More...
bool	first ()
	returns True if on the last element of the hash More...
bool	last ()
	returns True if on the first element of the hash More...
bool	next ()
	Moves the current position to the previous element in the hash; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the last element in the hash if the hash is not empty. More...
bool	prev ()
	Moves the current position to the next element in the hash; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the first element in the hash if the hash is not empty. More...
Public Member Methods inherited from Qore::HashIterator
	constructor (hash< auto > h)
	Creates the hash iterator object. More...
	constructor ()
	Creates an empty hash iterator object. More...
	copy ()
	Creates a copy of the HashIterator object, iterating the same object as the original and in the same position. More...
bool	empty ()
	returns True if the hash is empty; False if not More...
string	getKey ()
	returns the current key value or throws an INVALID-ITERATOR exception if the iterator is invalid More...
auto	getKeyValue ()
	returns the current value of the current hash key being iterated or throws an INVALID-ITERATOR exception if the iterator is invalid More...
auto	getValue ()
	returns the current key value or throws an INVALID-ITERATOR exception if the iterator is invalid More...
hash< auto >	getValuePair ()
	returns a hash with the current key and value (a hash with 2 keys: "key" and "value") or throws an INVALID-ITERATOR exception if the iterator is invalid More...
	reset ()
	Reset the iterator instance to its initial state. More...
bool	valid ()
	returns True if the iterator is currently pointing at a valid element, False if not More...

Detailed Description

This class an iterator class for hashes.

Call HashReverseIterator::next() to iterate through the hash in reverse order; do not use the iterator if HashReverseIterator::next() returns False. A hash can be iterated in reverse order by calling HashReverseIterator::prev() instead of HashReverseIterator::next()

Example: HashReverseIterator basic usage

hash<auto> h = ( "key1" : 1, "key2" : 2, );
 
HashReverseIterator it(h);
while (it.next()) {
    printf("getKey: %n; getKeyValue: %n; getValue: %n; getValuePair: %n\n",
           it.getKey(), it.getKeyValue(), it.getValue(), it.getValuePair());
}
 
getKey: "key2"; getKeyValue: 2; getValue: 2; getValuePair: hash: (key : "key2", value : 2)
getKey: "key1"; getKeyValue: 1; getValue: 1; getValuePair: hash: (key : "key1", value : 1)

Note

• In general, the HashReverseIterator class is not designed to be accessed from multiple threads; it was created without locking for fast and efficient use when used from a single thread. For methods that would be unsafe to use in another thread, any use of such methods in threads other than the thread where the constructor was called will cause an ITERATOR-THREAD-ERROR to be thrown.
• HashReverseIterator is functionally equivalent to HashIterator, but the effect of HashReverseIterator::next() and HashReverseIterator::prev() are the opposite of HashIterator::next() and HashIterator::prev(); that is HashReverseIterator::next() will iterate through the hash in reverse order, while HashReverseIterator::prev() iterates in forward order. Additionally the meanings of the return values for HashReverseIterator::first() and HashReverseIterator::last() are swapped in respect to HashIterator::first() and HashIterator::last().

See also

HashIterator

Member Function Documentation

constructor() [1/2]

Qore::HashReverseIterator::constructor

(

)

Creates an empty iterator object.

Example:

*hash<auto> h = get_hash_or_nothing();
HashReverseIterator hi(h);

constructor() [2/2]

Qore::HashReverseIterator::constructor

(

hash< auto >

h

)

Creates the hash iterator object.

Parameters

h	the hash to iterate

Example:

HashReverseIterator hi(h);

copy()

Qore::HashReverseIterator::copy

(

)

Creates a copy of the HashReverseIterator object, iterating the same object as the original and in the same position.

Example:

HashReverseIterator ni = i.copy();

first()

bool Qore::HashReverseIterator::first ( )

virtual

returns True if on the last element of the hash

Returns

True if on the last element of the hash

Code Flags:

CONSTANT

Example:

while (i.next()) {
    if (i.first())
        printf("START:\n");
}

Reimplemented from Qore::HashIterator.

last()

bool Qore::HashReverseIterator::last ( )

virtual

returns True if on the first element of the hash

Returns

True if on the first element of the hash

Code Flags:

CONSTANT

Example:

while (i.next()) {
    if (i.last())
        printf("END.\n");
}

Reimplemented from Qore::HashIterator.

next()

bool Qore::HashReverseIterator::next ( )

virtual

Moves the current position to the previous element in the hash; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the last element in the hash if the hash is not empty.

This method will return True again after it returns False once if the hash is not empty, otherwise it will always return False. The iterator object should not be used after this method returns False

Returns

False if there are no more elements in the hash (in which case the iterator object is invalid and should not be used); True if successful (meaning that the iterator object is valid)

Example:

while (i.prev()) {
    printf(" + %y\n", i.getValue());
}

Note

HashReverseIterator::next() is the opposite of HashIterator::next(); it is functionally equivalent to HashIterator::prev(); HashReverseIterator::next() iterates through the hash in reverse order

Exceptions

ITERATOR-THREAD-ERROR

this exception is thrown if this method is called from any thread other than the thread that created the object

Reimplemented from Qore::HashIterator.

prev()

bool Qore::HashReverseIterator::prev ( )

virtual

Moves the current position to the next element in the hash; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the first element in the hash if the hash is not empty.

This method will return True again after it returns False once if hash is not empty, otherwise it will always return False. The iterator object should not be used after this method returns False

Returns

False if there are no more elements in the hash (in which case the iterator object is invalid and should not be used); True if successful (meaning that the iterator object is valid)

Example:

while (i.next()) {
    printf(" + %y\n", i.getValue());
}

Note

HashReverseIterator::prev() is the opposite of HashIterator::prev(); it is functionally equivalent to HashIterator::next(); HashReverseIterator::prev() iterates through the hash in forward order

Exceptions

ITERATOR-THREAD-ERROR

this exception is thrown if this method is called from any thread other than the thread that created the object

Reimplemented from Qore::HashIterator.