2 Why We Need Model-Based Testing

166 Modeling Systems with Structured State
You can construct a sequence from any value that supports IEnumerable:
static Sequence ConvertToSequence(IEnumerable list)
{
return new Sequence(list);
}
Sequence queries
You can access the first and last element of a sequence using the Head and Last
properties.
The subsequence of all elements except the first is the Tail. The subsequence of
all elements except the last is the Front of the sequence.
Sequence squares = new Sequence(0, 1, 4, 9, 16, 25, 36);
Assert.AreEqual(squares.Head, 0);
Assert.AreEqual(squares.Last, 36);
Assert.AreEqual(squares.Tail.Head, 1);
Assert.AreEqual(squares.Front.Last, 25);
Assert.AreEqual(squares.Tail.Tail.Head, 4);
Sequences also provide for random access using the C# indexer. However, if your
primary mode of access is random, you should consider using the ValueArray type
instead of a sequence.
10.3.4 Value arrays
A value array is an ordered collection of (possibly repeating) elements. It is similar
to the .NET Array type, except that a value array is immutable. Unlike a .NET array,
a value array uses structural equality.
Sequences and value arrays are similar in the way that .NET lists and arrays are
similar. In other words, sequences are best for list-like iterative construction and
access. Value arrays work best when random access is the most common form of
access and when incrementally adding elements is not common.
Sequences appear more often than value arrays in most models, especially when
small numbers of elements are involved. Value arrays are useful for larger data sets
that require a lot of random access. Most models will not require them.
Appendix A.2.5 lists value array operations provided by the NModel library.
Value arrays are created from a .NET array:
string[] ratingsArr = new string[]{"Poor", "Average", "Excellent"};
ValueArray ratings = new ValueArray(ratingsArr);
Assert.AreEqual(ratings[2], "Excellent");
Random access is supported through the C# indexer.
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