Cgu::IntIter Class Reference

An iterator class providing a lazy integer range over a virtual container. More...

#include <c++-gtk-utils/parallel.h>

Public Types
typedef int	value_type
typedef int	reference
typedef void	pointer
typedef int	difference_type
typedef std::random_access_iterator_tag	iterator_category

Public Member Functions
	IntIter (value_type val_=0)
	IntIter (const IntIter &)=default
IntIter &	operator= (const IntIter &)=default
IntIter &	operator++ ()
IntIter	operator++ (int)
IntIter &	operator-- ()
IntIter	operator-- (int)
IntIter &	operator+= (difference_type n)
IntIter &	operator-= (difference_type n)
reference	operator[] (difference_type n) const
reference	operator* () const

Detailed Description

An iterator class providing a lazy integer range over a virtual container.

See also

IntIterHelpers

This class acts as an iterator which iterates over a range of integers lazily, as if over a virtual container of incrementing ints constructed using std::iota. It is principally intended for use in constructing parallel for loops using Cgu::Thread::parallel_for_each() or Cgu::Thread::parallel_transform(), which is why it is in the c++-gtk-utils/parallel.h header, but it can be used whenever a lazy range of integers is required.

It behaves as a random access iterator to const int, and has the normal increment, decrement and other random access functions. When used with Cgu::Thread::parallel_for_each() and Cgu::Thread::parallel_transform(), because it acts as an iterator to const int, the callable object passed to those functions must take an int or const int& argument. Any IntIter object compares equal to any other IntIter object which at the time in question references the same int value, so it can be used as the beginning iterator or end iterator of a range for a standard algorithm; and one IntIter object is less than another IntIter object if it references an int value less than the other, and so on as regards the other comparison operators.

Here is an example of its use with Cgu::Thread::parallel_transform(), as a parallelized equivalent of a for loop which increments a count integer on each iteration through the loop. In this example, the count integer, as incremented on each iteration, is squared and the result stored in a std::vector object (in practice you would not want to use this construction for such a trivial case as it would be slower than the single threaded version - it is for use where some significant work is done in the for loop, here represented by the lambda expression):

using namespace Cgu;
std::vector<int> v;
Thread::TaskManager tm{4};
Thread::parallel_transform(tm,
                           IntIter{0},   // beginning of range
                           IntIter{10},  // one past end of range
                           std::back_inserter(v),
                           [](int i) {return i * i;});
for (auto elt: v) std::cout << elt << ' ';
std::cout << std::endl;

Although unlikely to be useful very often, the iterator can count backwards using std::reverse_iterator:

using namespace Cgu;
typedef std::reverse_iterator<IntIter> RIntIter;
std::vector<int> v;
Thread::TaskManager tm{4};
Thread::parallel_transform(tm,
                           RIntIter{IntIter{10}},  // one past beginning of range
                           RIntIter{IntIter{0}},   // end of range
                           std::back_inserter(v),
                           [](int i) {return i * i;});
for (auto elt: v) std::cout << elt << ' ';
std::cout << std::endl;

Since 2.0.27.

Member Typedef Documentation

difference_type

typedef int Cgu::IntIter::difference_type

iterator_category

typedef std::random_access_iterator_tag Cgu::IntIter::iterator_category

pointer

typedef void Cgu::IntIter::pointer

reference

typedef int Cgu::IntIter::reference

value_type

typedef int Cgu::IntIter::value_type

Constructor & Destructor Documentation

IntIter() [1/2]

Cgu::IntIter::IntIter ( value_type  val_ = 0 )

inlineexplicit

This constructor acts as both a default constructor and an initializing constructor. It does not throw.

Since 2.0.27.

IntIter() [2/2]

Cgu::IntIter::IntIter ( const IntIter &  )

default

The copy constructor does not throw.

Since 2.0.27.

Member Function Documentation

operator*()

reference Cgu::IntIter::operator* ( ) const

inline

The dereferencing operator does not throw. No locking is carried out, so if the iterator is accessed in more than one thread and one calls a non-const method, the user must provide synchronization (but Cgu::Thread::parallel_for_each(), Cgu::Thread::parallel_for_each_partial(), Cgu::Thread::parallel_transform() and Cgu::Thread::parallel_transform_partial() only access source and destination iterators in the thread which calls the functions, so use of an IntIter object only by one of those functions does not require synchronization).

Returns

The integer value currently represented by the iterator.

Since 2.0.27.

operator++() [1/2]

IntIter& Cgu::IntIter::operator++ ( )

inline

The pre-increment operator does not throw. No locking is carried out, so if the iterator is accessed in more than one thread, the user must provide synchronization (but Cgu::Thread::parallel_for_each(), Cgu::Thread::parallel_for_each_partial(), Cgu::Thread::parallel_transform() and Cgu::Thread::parallel_transform_partial() only access source and destination iterators in the thread which calls the functions, so use of an IntIter object only by one of those functions does not require synchronization).

Returns

A reference to the iterator after being incremented.

Since 2.0.27.

operator++() [2/2]

IntIter Cgu::IntIter::operator++ ( int  )

inline

The post-increment operator does not throw. No locking is carried out, so if the iterator is accessed in more than one thread, the user must provide synchronization (but Cgu::Thread::parallel_for_each(), Cgu::Thread::parallel_for_each_partial(), Cgu::Thread::parallel_transform() and Cgu::Thread::parallel_transform_partial() only access source and destination iterators in the thread which calls the functions, so use of an IntIter object only by one of those functions does not require synchronization).

Returns

A copy of the iterator prior to being incremented.

Since 2.0.27.

operator+=()

IntIter& Cgu::IntIter::operator+= ( difference_type  n )

inline

This operator adds the value of the argument to the integer value currently represented by the iterator. It does not throw. No locking is carried out, so if the iterator is accessed in more than one thread, the user must provide synchronization (but Cgu::Thread::parallel_for_each(), Cgu::Thread::parallel_for_each_partial(), Cgu::Thread::parallel_transform() and Cgu::Thread::parallel_transform_partial() only access source and destination iterators in the thread which calls the functions, so use of an IntIter object only by one of those functions does not require synchronization).

Returns

A reference to the iterator after addition.

Since 2.0.27.

operator--() [1/2]

IntIter& Cgu::IntIter::operator-- ( )

inline

The pre-decrement operator does not throw. No locking is carried out, so if the iterator is accessed in more than one thread, the user must provide synchronization (but Cgu::Thread::parallel_for_each(), Cgu::Thread::parallel_for_each_partial(), Cgu::Thread::parallel_transform() and Cgu::Thread::parallel_transform_partial() only access source and destination iterators in the thread which calls the functions, so use of an IntIter object only by one of those functions does not require synchronization).

Returns

A reference to the iterator after being decremented.

Since 2.0.27.

operator--() [2/2]

IntIter Cgu::IntIter::operator-- ( int  )

inline

The post-decrement operator does not throw. No locking is carried out, so if the iterator is accessed in more than one thread, the user must provide synchronization (but Cgu::Thread::parallel_for_each(), Cgu::Thread::parallel_for_each_partial(), Cgu::Thread::parallel_transform() and Cgu::Thread::parallel_transform_partial() only access source and destination iterators in the thread which calls the functions, so use of an IntIter object only by one of those functions does not require synchronization).

Returns

A copy of the iterator prior to being decremented.

Since 2.0.27.

operator-=()

IntIter& Cgu::IntIter::operator-= ( difference_type  n )

inline

This operator subtracts the value of the argument from the integer value currently represented by the iterator. It does not throw. No locking is carried out, so if the iterator is accessed in more than one thread, the user must provide synchronization (but Cgu::Thread::parallel_for_each(), Cgu::Thread::parallel_for_each_partial(), Cgu::Thread::parallel_transform() and Cgu::Thread::parallel_transform_partial() only access source and destination iterators in the thread which calls the functions, so use of an IntIter object only by one of those functions does not require synchronization).

Returns

A reference to the iterator after subtraction.

Since 2.0.27.

operator=()

IntIter& Cgu::IntIter::operator= ( const IntIter &  )

default

The copy assignment operator does not throw. No locking is carried out, so if the iterator is accessed in more than one thread, the user must provide synchronization (but Cgu::Thread::parallel_for_each(), Cgu::Thread::parallel_for_each_partial(), Cgu::Thread::parallel_transform() and Cgu::Thread::parallel_transform_partial() only access source and destination iterators in the thread which calls the functions, so use of an IntIter object only by one of those functions does not require synchronization).

Since 2.0.27.

operator[]()

reference Cgu::IntIter::operator[] ( difference_type  n ) const

inline

The offset dereferencing operator does not throw. No locking is carried out, so if the iterator is accessed in more than one thread and one calls a non-const method, the user must provide synchronization (but Cgu::Thread::parallel_for_each(), Cgu::Thread::parallel_for_each_partial(), Cgu::Thread::parallel_transform() and Cgu::Thread::parallel_transform_partial() only access source and destination iterators in the thread which calls the functions, so use of an IntIter object only by one of those functions does not require synchronization).

Returns

The integer value at the given offset.

Since 2.0.27.

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

• parallel.h