Ordering Instances
The implementations of the collection classes’ sorting and searching
capabilities depend on certain facilities in the contained objects themselves.
The most common of these are the ability to order the contained objects (used
for sorting and efficient searching) and the ability to hash an object (to
speed storage and retrieval in dictionary-based structures such as Hashtable
).
As with most other parts of the FCL’s collections framework, this is
accomplished via standardized interfaces and overridden virtual methods on System.Object
.
The IComparable Interface
The IComparable
interface allows one object to indicate
it’s ordering relative to another instance of the same type. To allow
sorting and searching of your types in an array, implement the IComparable
interface,
which looks like this:
public interface IComparable { int CompareTo(object rhs); }
Implementation of this interface should follow the following semantic rules:
If
a
comes beforeb
→a.CompareTo(b) < 0
If
a
is equalb
→a.CompareTo(b) == 0
If
a
comes afterb
→a.CompareTo(b) > 0
null
comes first:a.CompareTo(null) > 0
a.CompareTo(b)
→a.GetType() == b.GetType()
An example implementation of this interface might look like this:
public sealed class Person : IComparable { public string Name; public int Age; public int CompareTo(object o) { // Check for null if (o==null) return 1; // Check for concrete type match if (o.GetType() != this.GetType()) throw new ArgumentException(); // Sort instances by ascending ...
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