Homework 2 review

1
Homework 2 review

• 09/20/02

2
Homework 1 reviewSolution

• using System
• using System.Collections
• using System.Diagnostics
• namespace BC.Core
• using Exceptions
• namespace Collections
• Serializable
• public class Set ICollection, ICloneable
• protected Hashtable S
• public Set ()
• S new Hashtable()
• public Set (object o)
• this()

3
Homework 1 reviewSolution (cont.)

• . . .
• public int Count
• get
• return S.Count
• public bool Empty
• get
• return Count 0
• public bool Contains (object o)
• return S.Contains(o)

4
Homework 1 reviewSolution (cont.)

• . . .
• public bool IsSynchronized
• get
• return S.Keys.IsSynchronized
• public object SyncRoot
• get
• return S.Keys.SyncRoot
• public void Add (object o)
• So null

5
Homework 1 reviewSolution (cont.)

• . . .
• public object Clone ()
• Set r new Set()
• foreach (object o in this)
• r.Add(o)
• return r
• public static bool isNull (Set s)
• return (object)s null
• public object Singleton
• get
• Debug.Assert(Count lt 1)
• foreach (object o in this)

6
Homework 1 reviewSolution (cont.)

• . . .
• public static bool operator lt (Set s1, Set
  s2)
• foreach (object o in s1)
• if (!s2.Contains(o))
• return false
• return true
• public static bool operator gt (Set s1, Set
  s2)
• return s2 lt s1
• public static bool operator (Set s1, Set
  s2)
• if (isNull(s1) isNull(s2))
• return isNull(s1) isNull(s2)
• else
• return s1 lt s2 s2 lt s1

7
Homework 1 reviewSolution (cont.)

• . . .
• public static Set operator (Set s1, Set s2)
• Set r new Set()
• foreach (object o in s1)
• if (s2.Contains(o))
• r.Add(o)
• return r
• public static Set operator (Set s1, Set s2)
• Set r new Set()
• foreach (object o in s1)
• r.Add(o)
• foreach (object o in s2)
• r.Add(o)
• return r
• public static Set operator - (Set s1, Set s2)

8
Homework 1 reviewSolution (cont.)

• . . .
• public override bool Equals (object o)
• Set s o as Set
• return s ! null this s
• public override int GetHashCode ()
• int r 0
• foreach (object o in this)
• r o.GetHashCode()
• return r
• public override string ToString ()
• string r "\n"
• foreach (object o in this)
• r string.Format("\t0\n", o)
• return r "\n"

9
Homework 1 reviewWhat was useful

• foreach
• Properties
• Operator overloading

10
Homework 1 reviewWhat not to do

• Write Java code in C
• It works, but that is not the point
• Use enumerators explicitly
• Use for when you can use foreach
• Propagate Equals and GetHashCode to the base
  class
• Make array operations take linear (or more) time
• Use a.dict.Keys in foreach instead of just a
• Write complex code when simple one is OK
• Build strings the old way , , ,

11
Homework 1 reviewA General Guideline

• Use conversions instead of overloading multiple
  versions of the same operator
• The long way
• Set operator (Set s, IEnumerable e)
• Set operator (IEnumerable e, Set s)
• Instead
• Set operator (Set s1, Set s2)
• implicit operator Set (IEnumerable e)