2 Why We Need Model-Based Testing

164 Modeling Systems with Structured State
An exception will be thrown if the requested key is not in the map. Normally,
you will want to use the ContainsKey method to check that the key is in the map
before doing the lookup.
You can combine the ContainsKey check and lookup into a single operation using
TryGetValue.
static string LookupState(string city)
{
Map cityState =
new Map("Athens", "GA", "Paris", "TX"};
string state;
return (cityState.TryGetValue(city, out state) ? state
: "Unknown state");
}
Iterating through maps
Maps support iteration through keys, values, or key value pairs:
Map cityLength =
new Map("Athens", 6, "Paris", 5};
foreach(string city in cityLength.Keys) /* ... */
foreach(int length in cityLength.Values) /* ... */
foreach(Pair keyValuePair in cityLength) /* ... */
The Keys and Values properties return sets. This means that when iterating
through values of a map, values associated with more than one key will only be
encountered once. The Pair data type is decribed in Section 10.3.6.
10.3.3 Sequences
A sequence is an ordered collection of (possibly repeating) elements. This is similar
to the .NET List type, except that a sequence is an immutable value. Operations to
add and remove elements result in new sequences instead of making changes to the
sequence given as the argument.
Another difference between sequences and the .NET list type is structural equality.
Two sequences are equal if they contain the same elements, in the same order. Lists
in .NET use reference equality instead of structural equality.
Appendix A.2.4 provides a reference of sequence operations provided by the
NModel library.
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