irange: introduce one-parameter variant of irange

this simplifies the use of boost::irange, as boost::irange( 0, foo );
may compile or not depending on the platform-specific integer type of
foo, requiring an explicit cast of 0 to decltype(foo).

doc/reference/ranges/irange.qbk

@@ -8,6 +8,10 @@
 [heading Prototype]
 
 ``
+template<class Integer>
+iterator_range< range_detail::integer_iterator<Integer> >
+irange(Integer last);
+
 template<class Integer>
 iterator_range< range_detail::integer_iterator<Integer> >
 irange(Integer first, Integer last);
@@ -37,4 +41,3 @@ Defined in the header file `boost/range/irange.hpp`
 Constant. Since this function generates a new range the most significant performance cost is incurred through the iteration of the generated range.
 
 [endsect]
-

include/boost/range/irange.hpp

@@ -231,6 +231,13 @@ namespace boost
             iterator_t(first, num_steps, step_size));
     }
 
+    template<typename Integer>
+    integer_range<Integer>
+    irange(Integer last)
+    {
+        return integer_range<Integer>(static_cast<Integer>(0), last);
+    }
+
 } // namespace boost
 
 #endif // include guard

test/irange.cpp

@@ -18,6 +18,23 @@
 
 namespace boost
 {
+    // Test an integer range with a step size of 1.
+    template<typename Integer>
+    void test_irange_impl(Integer last)
+    {
+        std::vector<Integer> reference;
+        for (Integer i = static_cast<Integer>(0); i < last; ++i)
+        {
+            reference.push_back(i);
+        }
+
+        std::vector<Integer> test;
+        boost::push_back(test, boost::irange(last));
+
+        BOOST_CHECK_EQUAL_COLLECTIONS( test.begin(), test.end(),
+                                       reference.begin(), reference.end() );
+    }
+
     // Test an integer range with a step size of 1.
     template<typename Integer>
     void test_irange_impl(Integer first, Integer last)
@@ -64,6 +81,22 @@ namespace boost
                                        reference.begin(), reference.end() );
     }
 
+    // Test driver function that for an integer range [first, last)
+    // drives the test implementation through various integer
+    // types.
+    void test_irange(int last)
+    {
+        test_irange_impl<signed char>(last);
+        test_irange_impl<unsigned char>(last);
+        test_irange_impl<signed short>(last);
+        test_irange_impl<unsigned short>(last);
+        test_irange_impl<signed int>(last);
+        test_irange_impl<unsigned int>(last);
+        test_irange_impl<signed long>(last);
+        test_irange_impl<unsigned long>(last);
+    }
+
+
     // Test driver function that for an integer range [first, last)
     // drives the test implementation through various integer
     // types.
@@ -102,6 +135,11 @@ namespace boost
     // number of implementation branches.
     void irange_unit_test()
     {
+        // Test the single-step version of irange(last)
+        test_irange(0);
+        test_irange(1);
+        test_irange(10);
+
         // Test the single-step version of irange(first, last)
         test_irange(0, 0);
         test_irange(0, 1);