Merge pull request #352 from jaredhoberock/documentation

Documentation

Author: jaredhoberock

thrust/functional.h

@@ -962,22 +962,116 @@ template<typename BinaryPredicate>
 /*! \}
  */
 
+
+/*! \addtogroup placeholder_objects Placeholder Objects
+ *  \ingroup function_objects
+ *  \{
+ */
+
+
+/*! \namespace placeholders
+ *  \brief Facilities for constructing simple functions inline.
+ *
+ *  Objects in the \p thrust::placeholders namespace may be used to create simple arithmetic functions inline
+ *  in an algorithm invocation. Combining placeholders such as \p _1 and \p _2 with arithmetic operations such as \c +
+ *  creates an unnamed function object which applies the operation to their arguments.
+ *
+ *  The type of placeholder objects is implementation-defined.
+ *
+ *  The following code snippet demonstrates how to use the placeholders \p _1 and \p _2 with \p thrust::transform
+ *  to implement the SAXPY computation:
+ *
+ *  \code
+ *  #include <thrust/device_vector.h>
+ *  #include <thrust/transform.h>
+ *  #include <thrust/functional.h>
+ *
+ *  int main()
+ *  {
+ *    thrust::device_vector<float> x(4), y(4);
+ *    x[0] = 1;
+ *    x[1] = 2;
+ *    x[2] = 3;
+ *    x[3] = 4;
+ *    
+ *    y[0] = 1;
+ *    y[1] = 1;
+ *    y[2] = 1;
+ *    y[3] = 1;
+ *
+ *    float a = 2.0f;
+ *
+ *    using namespace thrust::placeholders;
+ *
+ *    thrust::transform(x.begin(), x.end(), y.begin(), y.begin(),
+ *      a * _1 + 2
+ *    );
+ *
+ *    // y is now {3, 5, 7, 9}
+ *  }
+ *  \endcode
+ */
 namespace placeholders
 {
 
+
+/*! \p thrust::placeholders::_1 is the placeholder for the first function parameter.
+ */
 static const thrust::detail::functional::placeholder<0>::type _1;
+
+
+/*! \p thrust::placeholders::_2 is the placeholder for the second function parameter.
+ */
 static const thrust::detail::functional::placeholder<1>::type _2;
+
+
+/*! \p thrust::placeholders::_3 is the placeholder for the third function parameter.
+ */
 static const thrust::detail::functional::placeholder<2>::type _3;
+
+
+/*! \p thrust::placeholders::_4 is the placeholder for the fourth function parameter.
+ */
 static const thrust::detail::functional::placeholder<3>::type _4;
+
+
+/*! \p thrust::placeholders::_5 is the placeholder for the fifth function parameter.
+ */
 static const thrust::detail::functional::placeholder<4>::type _5;
+
+
+/*! \p thrust::placeholders::_6 is the placeholder for the sixth function parameter.
+ */
 static const thrust::detail::functional::placeholder<5>::type _6;
+
+
+/*! \p thrust::placeholders::_7 is the placeholder for the seventh function parameter.
+ */
 static const thrust::detail::functional::placeholder<6>::type _7;
+
+
+/*! \p thrust::placeholders::_8 is the placeholder for the eighth function parameter.
+ */
 static const thrust::detail::functional::placeholder<7>::type _8;
+
+
+/*! \p thrust::placeholders::_9 is the placeholder for the ninth function parameter.
+ */
 static const thrust::detail::functional::placeholder<8>::type _9;
+
+
+/*! \p thrust::placeholders::_10 is the placeholder for the tenth function parameter.
+ */
 static const thrust::detail::functional::placeholder<9>::type _10;
 
+
 } // end placeholders
 
+
+/*! \} // placeholder_objects
+ */
+
+
 } // end thrust
 
 #include <thrust/detail/functional.inl>

thrust/iterator/iterator_adaptor.h

@@ -55,57 +55,46 @@ namespace thrust
  *  functionality, it is occasionally more straightforward to derive from \p iterator_adaptor directly.
  *
  *  To see how to use \p iterator_adaptor to create a novel iterator type, let's examine how to use it to
- *  define our own version of \p transform_iterator, a fancy iterator which fuses the application of
- *  a unary function with an iterator dereference:
+ *  define \p repeat_iterator, a fancy iterator which repeats elements from another range a given number of time:
  *
  *  \code
  *  #include <thrust/iterator/iterator_adaptor.h>
  *
- *  // derive my_transform_iterator from iterator_adaptor
- *  template<typename Function, typename Iterator>
- *    class my_transform_iterator
+ *  // derive repeat_iterator from iterator_adaptor
+ *  template<typename Iterator>
+ *    class repeat_iterator
  *      : public thrust::iterator_adaptor<
- *          my_transform_iterator<Function, Iterator>, // the first template parameter is the name of the type we're creating
- *          Iterator,                                  // the second template parameter is the name of the iterator we're adapting
- *          typename Function::result_type,            // the third template parameter is the name of the iterator's value_type -- it's simply the function's result_type.
- *          thrust::use_default,                       // the fourth template parameter is the name of the iterator's system. use_default will use the same system as the base iterator.
- *          thrust::use_default,                       // the fifth template parameter is the name of the iterator's traversal. use_default will use the same traversal as the base iterator.
- *          typename Function::result_type             // the sixth template parameter is the name of the iterator's reference. Like value_type, it's simply the function's result_type.
+ *          repeat_iterator<Iterator>, // the first template parameter is the name of the iterator we're creating
+ *          Iterator                   // the second template parameter is the name of the iterator we're adapting
+ *                                     // we can use the default for the additional template parameters
  *        >
  *  {
  *    public:
  *      // shorthand for the name of the iterator_adaptor we're deriving from
  *      typedef thrust::iterator_adaptor<
- *        my_transform_iterator<Function, Iterator>,
- *        Iterator,
- *        typename Function::result_type,
- *        thrust::use_default,
- *        thrust::use_default,
- *        typename Function::result_type
+ *        repeat_iterator<Iterator>,
+ *        Iterator
  *      > super_t;
  *
  *      __host__ __device__
- *      my_transform_iterator(const Iterator &x, Function f) : super_t(x), m_f(f) {}
- *
- *      // other assorted constructors might go here
- *      ...
+ *      repeat_iterator(const Iterator &x, int n) : super_t(x), begin(x), n(n) {}
  *
  *      // befriend thrust::iterator_core_access to allow it access to the private interface below
  *      friend class thrust::iterator_core_access;
  *
  *    private:
- *      // here we define what it means to dereference my_transform_iterator
+ *      // repeat each element of the adapted range n times
+ *      unsigned int n;
+ *
+ *      // used to keep track of where we began
+ *      const Iterator begin;
+ *
  *      // it is private because only thrust::iterator_core_access needs access to it
  *      __host__ __device__
  *      typename super_t::reference dereference() const
  *      {
- *        // when my_transform_iterator is dereferenced, it dereferences the base iterator
- *        // and applies the unary function
- *        return m_f(*this->base());
+ *        return *(begin + (this->base() - begin) / n);
  *      }
- *
- *      // the unary function
- *      Function m_f;
  *  };
  *  \endcode
  *
@@ -116,6 +105,10 @@ namespace thrust
  *  The exception is Thrust's addition of the template parameter \p System, which is necessary to allow Thrust
  *  to dispatch an algorithm to one of several parallel backend systems.
  *
+ *  \p iterator_adaptor is a powerful tool for creating custom iterators directly. However, the large set of iterator semantics which must be satisfied
+ *  for algorithm compatibility can make \p iterator_adaptor difficult to use correctly. Unless you require the full expressivity of \p iterator_adaptor,
+ *  consider building a custom iterator through composition of existing higher-level fancy iterators instead. 
+ *
  *  Interested users may refer to <tt>boost::iterator_adaptor</tt>'s documentation for further usage examples.
  */
 template<typename Derived,