C# 4 and .NET 4

140 ❘ ChaPTer 6 ArrAys And tuples
arraysegment < T >
The struct ArraySegment < T > represents a segment of an array. If parts of an array should be returned
from or passed to a method, a segment can be used. Instead of passing the array, offset, and count with
separate parameters to a method, you can pass a single parameter with ArraySegment < T > . With this
structure the information about the segment (the offset and count) is contained within the members of
the structure.
The method SumOfSegments takes an array of ArraySegment < int > elements to calculate the sum of all the
integers that are defi ned with the segments and returns the sum:
static int SumOfSegments(ArraySegment < int > [] segments)
{
int sum = 0;
foreach (var segment in segments)
{
for (int i = segment.Offset; i < segment.Offset +
segment.Count; i++)
{
sum += segment.Array[i];
}
}
return sum;
}
code snippet ArraySegmentSample/Program.cs
This method is used by passing an array of segments. The fi rst array element references three elements of
ar1 starting with the fi rst element; the second array element references three elements of ar2 starting with
the fourth element:
int[] ar1 = { 1, 4, 5, 11, 13, 18 };
int[] ar2 = { 3, 4, 5, 18, 21, 27, 33 };
var segments = new ArraySegment < int > [2]
{
new ArraySegment < int > (ar1, 0, 3),
new ArraySegment < int > (ar2, 3, 3)
};
var sum = SumOfSegments(segments);
It ’ s important to note that array segments don ’ t copy the elements of the originating
array. Instead, the originating array can be accessed through ArraySegment < T > . If
elements of the array segment are changed, the changes can be seen in the original
array.
enumeraTions
By using the foreach statement you can iterate elements of a collection (see Chapter 10) without
the need to know the number of elements inside the collection. The foreach statement uses an
enumerator. Figure 6 - 7 shows the relationship between the client invoking the foreach method and
the collection. The array or collection implements the IEnumerable interface with the
GetEnumerator() method. The GetEnumerator() method returns an enumerator implementing
www.it-ebooks.info